Generalised UK habit data for use in radiological impact assessments
Published 30 September 2026
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Executive summary
Estimating the radiation dose to a representative person requires an understanding of their habits, such as how much food and water they consume, their breathing rate, how long they spend near sources of radioactivity, and how much material they inadvertently ingest. Such information is collectively referred to as habit data.
Ideally, radiological impact assessments should use site-specific habit data that reflects the behaviours of people who may be exposed. In practice, this information is not always available so the UK Health Security Agency (UKHSA) and its predecessor organisations have published generalised UK population habit data, which can be used in assessments when site-specific data is limited. This report is the latest publication in that series and replaces the previous publication (1).
The information in this report is intended for use to support the estimation of radiation doses to a representative person whose habits are typical of the general UK population. It is recognised that these habits may not reflect local variations, for example due to the availability of some foods or access to amenities. The data in this report should therefore be used to supplement any site-specific data, rather than replace it, unless there is good reason to do so. Where generalised data is used, the impact of the results should be reviewed as part of the tiered assessment process.
Following ICRP recommendations on the definition of the representative person, this report presents habit data for 3 age groups: 1 year old infants, 10 year old children and adults. For each age group, the report includes typical and high-rate values, with guidance on selecting the most appropriate value to use.
1. Introduction
Assessments of the radiological impact to members of the public from radioactivity present in the environment are carried out in several situations, including planning new facilities, authorising discharges of radioactive wastes from existing sites, and demonstrating that any radioactivity left in situ at the time of surrender of nuclear site licences represents a suitably low level of risk. These assessments rely on a wide range of information related to both the characteristics of the radioactive source as well as the habits of people who may be exposed.
In this context, habits relate to numerical values that define a person’s activities, such as how long they spend in certain locations, how much food and water they consume, and their breathing rate. Ideally, radiological impact assessments should use habits that have been observed in the exposed population. In the UK, some site-specific habit data is available from surveys that are regularly performed around nuclear licensed sites. Even where such data is available, it often includes a relatively small number of surveyed individuals with large uncertainties and may represent only certain demographics or timeframes. Where no surveys have been performed, site-specific habit data is likely to be limited or unavailable. Some assessments will also have to consider what habits may reasonably arise in the future, for example when assessing doses resulting from future disposals of radioactive waste. Where site-specific habit data does not exist, assumptions must be made about what habits individuals within the exposed population may have.
Since habits vary between individuals, a practical approach taken in radiation assessments is to estimate the dose to a representative person, rather than to a specific individual. The representative person is defined by the International Commission on Radiological Protection (ICRP) as a hypothetical individual who has characteristics that are representative of the more highly exposed individuals in the population (2). It is important that the quantities used to define the habits of a representative person are realistic and sustainable in the area where exposure to radiation may occur.
To make best use of available data and resources while accounting for uncertainties, radiological impact assessments should use a tiered approach. This begins with an initial assessment using available data, supplemented with cautious but realistic assumptions, to provide a conservative estimate of the dose. If decisions cannot be made on the results of that initial assessment, the assumptions and data should be reviewed to identify where improvements could realistically be made, for example by using a more accurate dispersion model or collecting more representative habit data. This process to refine the assessment is then repeated as required to produce a robust estimate of the radiation dose received.
To support the tiered approach to assessments, UKHSA and its predecessor organisations have published recommended habit data for use in defining the characteristics of a representative person in initial assessments (1, 3). This report updates the previous recommendations published in 2003 (NRPB-W41) (1) and includes data on food and water consumption, occupancy rates in locations commonly included in radiological impact assessments, inadvertent ingestion of environmental media, and inhalation rates.
The previous report (1) included both average (mean and median) and higher values (95th and 97.5th percentile), with the higher values intended to be used to define the habits of the critical group, now referred to as the representative person (4). These higher values are not intended to be used to define all characteristics of a representative person as this would not be realistic or sustainable. To support more balanced assessments, average habits are provided for use where typical values are more appropriate. In this report, habit data are presented as either typical (mean and median) or high-rate values, with additional guidance on selecting the most appropriate value in certain situations.
As recommended by ICRP, the representative person is defined as an individual who is aged 1 year (infant), 10 years (child), or an adult at the time of exposure (4). These age groups were chosen to account for how age-related changes in habits and physiological processes can impact the radiation dose received. The recommended habits are intended to be used directly with ICRP intake dose coefficients corresponding to these age groups, as published by ICRP (5).
Table 1. Representative age groups considered in radiological impact assessments
| Age in years | Age name | Habit data |
|---|---|---|
| 0 to 5 | Infant | 1 year old infant |
| 6 to 15 | Child | 10 year old child |
| 16 to 70 | Adult | Adult |
Section 2 of this report presents recommended food and water consumption rates for a representative member of the UK population. Section 3 presents recommended occupancy rates for locations that are commonly considered in radiological impact assessments. Section 4 outlines rates for the inadvertent ingestion of environmental media such as water, soil and sediment. Finally, Section 5 presents recommended inhalation rates that can be used directly or scaled to account for different activities undertaken in the presence of airborne radioactive material.
2. Consumption rates of foods and drinking water
When people consume food and water containing radioactive material, it contributes to the total radiation dose they receive (6). National diet and nutrition surveys (NDNS), carried out by Public Health England (PHE, now UKHSA) and the Food Standards Agency (FSA) (7 to 9), along with surveys of infants and young children (DNSIYC) by the Department of Health and FSA (10), were used to derive the representative consumption rates for the UK population. As these surveys were conducted for several years between 2008 and 2016, they are considered to represent not only current dietary habits but also to adequately account for changes likely to occur over a timeframe of several decades.
The consumption rates presented in this report are appropriate for use in assessments involving populations of more than a few tens of individuals over periods of up to several decades. As the size of the exposed population decreases, or the timeframe over which doses are to be assessed increases, uncertainties in habits are likely to increase, making the recommended habit data less representative. In such situations, while the recommended habits can still be used, results should be interpreted with caution.
2.1. Food and water categories
The recommended food consumption rates in this report are given by food category rather than individual food item. This approach is used for 2 reasons: food consumption surveys rely on self-reporting of diets, which can be vague or biased; and it matches how activity concentrations in food are usually modelled.
The food categories used are based on the NDNS and DNSIYC surveys, and the previous report (1). A comparison between the current categories and those in NRPB-W41 (1) is given in Table 2. It was not always possible to carry out a straightforward comparison and, in some cases, it was necessary to redefine the foods included in the categories. For example, fruit is now reported as hard and soft varieties, and potatoes and root vegetables are also presented separately, each pair can be combined if required.
Some food categories from NRPB-W41 have not been included: imported fruit and vegetables, mushrooms, honey and combined food groups. Imported produce was excluded as the location of origin is unknown, making it unsuitable for location-specific radiological assessments. It was also not possible to compare ‘butter’ and ‘oils and fats’ as separate categories, as the NDNS data combined these into one category. Instead, the NRPB-W41 value for ‘oils and fats’ has been compared to the NDNS data for ‘butter, oils and fats’.
Some new foods were identified but have not been included, as they only form a small part of the UK diet, although these foods may become more important in the future, such as meat alternatives and non-dairy milk types.
Table 2. Comparison of food categories given in NRPB-W41 and DNSIYC and NDNS surveys
| This report | NRPB-W41 |
|---|---|
| Terrestrial food | |
| Beef and beef products | Beef |
| All cuts of meat. Manufactured beef and veal products, including homemade recipe dishes, ready meals, canned beef products and pastrami. Dripping or beef fat | All beef |
| Cereals | Cereals |
| Breads, flours, buns, cakes and pastries, savoury biscuits, sweet biscuits, chocolate biscuits, breakfast cereals, other cereal products, pasta, pizza, wheat, oats, cornmeal, barley, rye, buckwheat, millet, sorghum | Wheat, oatmeal, buckwheat, semolina, millet, oats, cornmeal, pearl barley, cornflower, soya flour, sago, bran wheat, tapioca, rice and barley |
| Eggs and egg dishes | Eggs |
| All eggs | All eggs |
| Fat and oils | Butter |
| Fats, spreads (not butter) and oils. | All butter. Oils and fats. Dishes containing more than 10% fat or oil |
| Fruit (hard) | Fruit (domestic) |
| Rhubarb, quince, pear, apple | Pears, apples, cherries, plums, peaches, blackcurrants, redcurrants, blackberries, raspberries, gooseberries, strawberries, apricots, loganberries, prunes, rhubarb, damsons, whitecurrants, juice parts, jam part |
| Fruit (soft) | |
| Cherry, rosehip, blackcurrant, gooseberry, loganberry, mulberry, redcurrant, whitecurrant, elderberry, apricot, raspberry, strawberry, blueberry, bilberry, plum, blackberry | |
| Game | Game |
| Duck, goose, partridge, grouse, pheasant, venison and rabbit | Hare, rabbit, venison, ducks, geese and waders |
| Lamb, mutton and lamb products | Sheep |
| Lamb and mutton and manufactured products containing lamb | Mutton and lamb |
| Milk (cows) | Milk |
| All types of cow’s milk, evaporated milk, condensed milk. | All types of milk (full fat, semi-skimmed, goats milk, soya milk and so on) |
| Milk products | Other milk products |
| Cheese, yogurt, butter, fromage frais, crème fraiche, buttermilk, Kefir, sour cream, cream from cow’s milk | No comparison |
| Mushrooms | Mushrooms |
| Included in ‘Other vegetables’ | All mushrooms |
| Nuts and seeds | Nuts |
| Walnuts, almonds, pine nuts, pistachio nuts, hazelnuts, cashew nuts, Brazil nuts, pecan nuts, betel nuts, Barcelona nuts, macadamia nuts, peanuts, sesame seeds, pumpkin seeds, poppy seeds, sunflower seeds, cumin seeds, fennel seeds, caraway seeds, coriander seeds, hemp seeds, includes recipes; may contain some of the same foods as other groups | Brazil, peanut, pistachio, walnut, almonds, cashew, coconuts, hazel, pecan and chestnuts |
| Offal (cow) | Offal |
| Liver, brain, kidneys, heart, tripe | Brain, heart, sweetbread, liver, kidney, tongue, tripe, trotters, black pudding, faggots, haggis, haslet, white pudding |
| Offal (sheep) | |
| Sweetbread, liver, kidneys, haggis, any other sheep offal | See Offal |
| Pork and pork products | Pork |
| All meat cuts. Dripping or pig fat included | Including bacon and ham |
| Potatoes | Potatoes |
| All potatoes, sweet potato not included. Manufactured potato products, including crisps, and potato ready meals and takeaways | Crisps, canned and bottled potatoes, new and old potatoes, potato salad, jacket potatoes, chips and dried potatoes |
| Poultry | Poultry |
| Chicken, turkey, duck, goose, grouse, partridge, pheasant, pigeon, guinea fowl | Turkey, chicken, and wild fowl |
| Pulses | |
| Chickpeas, lentils, green lentils, brown lentils, lentils split, split peas, pigeon pea, aduki beans, kidney beans, blackeye beans, black bean, mung beans, butter beans, haricot beans and soya beans | Previously included in other domestic vegetables |
| Sugars and confectionery | Sugar |
| Chocolate confectionery, sugar confectionery, sugars and sweeteners | Pure sugar, black treacle, golden syrup, sugar confectionery, and marmalades |
| Tap water | Water intake rates |
| Tap water, concentrated soft drinks, tea and coffee | Tap water |
| Vegetables (green) | Green vegetables |
| Asparagus, broccoli, fennel, celery, globe artichokes, rocket, lettuce, sprouts, peas, cabbage (including kale, greens), spinach, watercress, chard, endive, chicory, courgette, leeks, cucumber, herbs, green beans, broad beans, runner beans and mange tout | Courgettes, marrow, Chinese leaves, watercress, endive, globe artichokes, asparagus, parsley, kohl rabi, cucumbers, lettuce, spinach, Brussel sprouts, cress, okra, broccoli, cauliflower and cabbage |
| Vegetables (other) | Other domestic vegetables |
| Mushrooms, aubergine, peppers, red cabbage, cauliflower, tomatoes. | Broad beans, beansprouts, French beans, kidney beans, runner beans, tomatoes (not tinned), sweetcorn, aubergine, peppers, peas, mange tout, haricot beans, pinto beans, lentils, garlic |
| Vegetables (root) | Root vegetables |
| Yam, turnip, swede, ginger, sweet potato, butternut squash, pumpkin, Jerusalem artichoke, parsnip, garlic, onion, beetroot, carrot, radish, celeriac, turmeric, salsify and cassava | Radishes, beetroot, parsnips, salsify, yams, swedes, turnips, chicory, fennel, celeriac, horseradish, onion, carrots, leeks, celery, Jerusalem artichoke |
| Aquatic foods | |
| Crustaceans (marine) | Crustaceans |
| Crabs, lobsters, prawns and shrimps | Crabs, lobsters, shrimps and prawns |
| Fish (freshwater) | Fish (freshwater) |
| Trout (river and sea) and river cobbler | Rainbow trout, brown trout |
| Fish (marine) | Fish (marine) |
| Mackerel, sardines, anchovies, salmon, pilchards, cod, haddock, bloater, kipper, whitebait, halibut, sole, plaice, whiting, skate, monkfish, rock salmon or dogfish, pollock, huss, coley and sea bass | Cod, haddock, hake, flounder, dab, sole, plaice halibut, dogfish, skate, ray, pollack, saithe, whiting, bass, mackerel, sea trout, salmon, mullet, herring, whitebait, sprat, twaite shad, allice shad and eels |
| Molluscs (marine) | Molluscs |
| Clams, cockles, mussels, oysters, whelks, winkles, scallops, octopus, squid, cuttlefish | Cockles, winkles, mussels, limpets, whelks, oysters |
2.2 Food and water consumption rates
Recommended typical and high consumption rates for each food group and water are presented in Tables 3 to 5 for infants, children and adults, respectively. As distributions in consumption rates are often skewed, median values are generally used to represent typical consumption. The median is the middle value in a distribution and is less affected by extreme values, making it a realistic estimate for most food groups. However, mean values are also included for situations where a more cautious estimate is needed, such as when a particular group in the population consumes a food group in larger amounts. In these situations, the mean is higher than the median, but not as conservative as the 97.5th percentile, which represents high consumption. Although the 97.5th percentile is deliberately cautious, it is still considered appropriate for use in initial assessments given the generic nature of the food categories and the range of situations the values are used for, including prospective assessments.
To highlight the generic nature of the recommended consumption rates, all rates have been rounded so that undue precision is not implied. Consumption rates equal to or less than 10 kg y-1 were rounded to 1, 5 or 10 kg y-1; rates between 11 to 99 kg y-1 were rounded to the nearest 5 kg y-1; and rates exceeding 100 kg y-1 to the nearest 10 kg y-1.
2.2.1 Food and water consumption rates by infants
Table 3 presents consumption rates for a representative infant, based on data from individuals aged 4 to 18 months in the DNSIYC surveys.
Typically, the dose to a breast-fed infant is not assessed unless specific radionuclides are present as the dose would not be significantly greater than that to one of the other age groups (11). As such, Table 3 does not include data for breast-fed infants. Where needed, the dose to a representative breast-fed infant should be calculated using the guidance in RCE-5 (11), with a typical or high breast milk consumption rate of 150 L y-1 or 420 L y-1, respectively, corresponding to the median and 97.5th percentile values from the DNSIYC data set.
DNSIYC data also shows that 10% of infants up to 3 months old consume approximately 20mL of tap water a day, mainly used to reconstitute formula (12). For infants aged 6 to 12 months, consumption of 800 to 1,000mL of tap water per day is recommended (13). These values could be applied if this age group is being considered.
Table 3. Consumption rates of food and water by infants
| Food group | Typical rate (kg or L y-1) |
High rate (kg or L y-1) |
|
|---|---|---|---|
| Median | Mean | 97.5th percentile | |
| Terrestrial foods | |||
| Beef and beef products | 5 | 5 | 15 |
| Cereals | 25 | 30 | 80 |
| Eggs and egg dishes | 1 | 5 | 20 |
| Fats and oils | 1 | 1 | 5 |
| Fruit (hard) | 10 | 15 | 55 |
| Fruit (soft) | 1 | 1 | 20 |
| Game | 1 | 1 | 5 |
| Lamb, mutton and lamb products | 1 | 5 | 10 |
| Milk (cows) | 35 | 75 | 250 |
| Milk products | 10 | 15 | 45 |
| Nuts and seeds | 0.5 | 1 | 5 |
| Offal (cow) | 1 | 1 | 5 |
| Offal (sheep) | 1 | 1 | 10 |
| Pork and pork products | 1 | 5 | 15 |
| Potatoes | 10 | 15 | 40 |
| Poultry | 1 | 1 | 10 |
| Pulses | 1 | 5 | 15 |
| Sugars and confectionery | 1 | 1 | 10 |
| Tap water | 40 | 55 | 230 |
| Vegetables (green) | 5 | 5 | 20 |
| Vegetables (other) | 5 | 10 | 30 |
| Vegetables (root) | 10 | 10 | 30 |
| Aquatic foods | |||
| Crustaceans (marine) | 1 | 1 | 5 |
| Fish (freshwater) | 5 | 5 | 10 |
| Fish (marine) | 1 | 5 | 10 |
| Molluscs (marine) | 1 | 1 | 5 |
2.2.2 Food and water consumption rates by children
Consumption rates for a representative child are presented in Table 4. In NRPB-W41 (1), recommended consumption rates for children were given for two age groups: 10 to 11 years and 14 to 15 years. In this report, a single age group is used to match the ICRP guidance on defining the representative person (4). However, to account for variations in the diet of individuals aged around 10 years, and to provide suitable robustness to the recommendations, ingestion rates by children in Table 4 are based on NDNS data for individuals aged 6 to 15 years.
Table 4. Consumption rates of food and water by children
| Food group | Typical rate (kg or L y-1) |
High rate (kg or L y-1) |
|
|---|---|---|---|
| Median | Mean | 97.5th percentile | |
| Terrestrial foods | |||
| Beef and beef products | 5 | 10 | 25 |
| Cereals | 80 | 80 | 150 |
| Eggs and egg dishes | 1 | 5 | 20 |
| Fats and oils | 1 | 1 | 15 |
| Fruit (hard) | 15 | 25 | 110 |
| Fruit (soft) | 1 | 5 | 30 |
| Game | 5 | 5 | 15 |
| Lamb, mutton and lamb products | 5 | 10 | 25 |
| Milk (cows) | 60 | 75 | 220 |
| Milk products | 10 | 15 | 50 |
| Nuts and seeds | 1 | 1 | 10 |
| Offal (cow) | 5 | 1 | 5 |
| Offal (sheep) | 1 | 1 | 10 |
| Pork and pork products | 5 | 10 | 30 |
| Potatoes | 25 | 30 | 70 |
| Poultry | 10 | 10 | 30 |
| Pulses | 5 | 5 | 20 |
| Sugars and confectionery | 5 | 10 | 40 |
| Tap water | 140 | 170 | 500 |
| Vegetables (green) | 5 | 10 | 30 |
| Vegetables (other) | 15 | 20 | 60 |
| Vegetables (root) | 5 | 10 | 30 |
| Aquatic foods | |||
| Crustaceans (marine) | 1 | 1 | 10 |
| Fish (freshwater) | 5 | 10 | 20 |
| Fish (marine) | 5 | 5 | 15 |
| Molluscs (marine) | 5 | 5 | 15 |
2.2.3 Food and water consumption rates by adults
Recommended consumption rates of food by UK adults are presented in Table 5. These consumption rates are based on NDNS data for individuals aged 16 to 70 years.
Table 5. Consumption rates of food and water by adults
| Typical rate (kg or L y-1) |
High rate (kg or L y-1) |
||
|---|---|---|---|
| Food group | Median | Mean | 97.5th percentile |
| Terrestrial foods | |||
| Beef and beef products | 10 | 15 | 35 |
| Cereals | 70 | 75 | 160 |
| Eggs and egg dishes | 5 | 10 | 30 |
| Fats and oils | 1 | 5 | 15 |
| Fruit (hard) | 10 | 20 | 80 |
| Fruit (soft) | 1 | 5 | 40 |
| Game | 10 | 20 | 30 |
| Lamb, mutton and lamb products | 10 | 15 | 35 |
| Milk (cows) | 55 | 65 | 200 |
| Milk products | 10 | 15 | 60 |
| Nuts and seeds | 1 | 1 | 15 |
| Offal (cow) | 5 | 5 | 15 |
| Offal (sheep) | 5 | 10 | 25 |
| Pork and pork products | 10 | 10 | 35 |
| Potatoes | 30 | 35 | 85 |
| Poultry | 10 | 15 | 40 |
| Pulses | 5 | 10 | 35 |
| Sugars and confectionery | 5 | 10 | 35 |
| Tap water | 300 | 340 | 910 |
| Vegetables (green) | 10 | 15 | 50 |
| Vegetables (other) | 25 | 35 | 100 |
| Vegetables (root) | 10 | 15 | 55 |
| Aquatic foods | |||
| Crustaceans (marine) | 5 | 5 | 25 |
| Fish (freshwater) | 15 | 15 | 30 |
| Fish (marine) | 10 | 10 | 35 |
| Molluscs (marine) | 5 | 5 | 25 |
2.2.4 Comparison of food and water consumption rates with NRPB-W41
Recommended consumption rates for all age groups, presented in Tables 3 to 5, are like those in NRPB-W41 for the most radiologically significant food and water groups. Where consumption rates differ from those in NRPB-W41, differences are generally within a factor of 2. The largest differences are associated with mean and median values, rather than the high-rate values. This is due to the relatively low values, the decision to round values in this report rather than imply undue precision, and minor changes in dietary habits over time as reported in national diet surveys.
A comparison of food intakes for adults found that the consumption of lamb and lamb products, root vegetables, cereals and sugar had increased, while consumption of fats, oils and potatoes has decreased. The table now includes typical and high-rate values for freshwater fish, molluscs and tap water which were not in the previous report. Additionally, more recent data allows for recommended consumption rates of shellfish and freshwater fish by infants to be given.
It is recognised that the recommended high-rate tap water consumption rates for infants and children in this report are lower than those recommended by some international bodies. For example, the recommended high-rate for an infant of 230 L y-1 is lower than 274 L y-1 recommended by the World Health Organization (WHO) and the 365 L y-1 recommended by the European Food Standards Agency (EFSA). These also differ from the values in NRPB-W41, which were based on ICRP guidance (14). The main reason for these differences lies in what the numbers represent. The WHO and EFSA rates represent guideline rates for a healthy diet, while the NRPB-W41 rates were derived from a consideration of physiological and metabolic processes, including total water balance, and the volume of water required per kcal expended. In contrast, the rates presented in Tables 3 to 5 are based on observation. It is therefore unsurprising that actual tap water consumption rates are lower than those derived using theoretical diets, as individuals often consume less water than recommended, and consumed liquids are obtained from multiple sources, of which tap water is only one.
2.3. Guidance on use of food consumption data
A radiological impact assessment should not assume that all foods are consumed at high rates, as this would result in unrealistic and unsustainable calorific intake. To determine which foods should be assessed using typical or high consumption rates, guidance from the National Dose Assessment Working Group (NDAWG) should be followed (15). The NDAWG guidance recommends that it should be assumed that the two foods contributing most to the total dose of a representative person should be consumed at high rates, while any other food should be consumed at typical rates. This approach minimises the impact of including an unsustainable and unrealistic diet, while also reducing the risk that the total dose is underestimated by ensuring radiologically significant foods are assessed using appropriately high consumption rates.
An assessment may also need to account for what fraction of consumed food comes from the contaminated environment. This depends on several factors, including the amount of food that may be produced in the contaminated environment; whether the food undergoes processing that mixes contaminated and uncontaminated produce, and how easily people can obtain locally produced food, such as from a local farm shop. As these factors are site-specific, the fraction of contaminated food should be determined separately for each assessment. However, for an initial assessment it is reasonable to assume that all food consumed originates from the contaminated environment to avoid underestimating the dose.
Finally, an assessment may need to account for the time between harvest and consumption as radioactive decay can significantly reduce the activity that is ingested, particularly for short-lived radionuclides. Guidance on delay times for different foods is described in (16).
3. Occupancy rates
The magnitude of radiation doses an individual receives from external, inhalation, and inadvertent ingestion exposure pathways is directly related to the amount of time spent in a contaminated environment. For example, the time spent in a location with airborne radioactivity affects both how much activity is inhaled and the level of external exposure to gamma radiation from airborne sources. Reduced indoor dose rates, due to shielding provided by buildings (17), highlight that radiological impact assessments should also consider the amount of time spent in different parts of a contaminated area, particularly when distinguishing between indoor and outdoor occupancy.
This section presents occupancy rates that can be used to estimate the dose to a representative person exposed to radiation in some commonly assessed locations such as the home, school, and workplace. Where assessments require an estimate of the dose to an individual exposed to radiation in multiple locations, occupancy rates may be determined using the values provided here as a guide.
3.1. Occupancy rates in terrestrial environments
3.1.1. Occupancy rates for stay-at-home individuals
Some individuals, such as stay-at-home parents, home-workers, young children and the elderly, may spend most of their time at home, although occasional periods spent away, such as for holidays, would be expected. To account for the possible presence of such individuals in the exposed population, it is recommended that a stay-at-home representative person spends 8,000 h y-1 in the vicinity of their home, corresponding to approximately 90% of their available time. For the remaining 10%, it is reasonable to assume they are far enough away to receive no additional dose from radioactivity in their usual residential environment.
Although most of the time at home would be spent indoors, some time outdoors should also be considered. For an initial assessment of a representative stay-at-home person of any age, it is recommended to assume that 500 h y-1 is outdoors within the home environment. This time is equivalent to approximately 3 hours a day over a 6-month period, representing individuals who spend longer periods of time outdoors during warmer months such as keen gardeners, children and infants. Alternatively, it could represent an individual who spends 1 to 2 hours outdoors every day of the year, such as a regular dog walker. The remaining 7,500 h y-1 is time spent indoors at home (Table 6).
Where contamination is limited in extent, such as being within the boundaries of a single property, the reasonableness of the occupancy rates should be reviewed and adjusted as necessary, as part of the tiered assessment process.
3.1.2. Occupancy rates for children at school
According to the Department for Education (18), UK state schools should deliver a minimum 32.5 hours of core school time per week, which includes classroom learning, outdoor play and physical education. With a minimum of 190 school days a year (19), a typical child spends approximately 1,250 h y-1 at school.
The government’s school action plan (20) recommends that children should engage in moderate-to-vigorous physical activity for an average of 60 minutes per day, a significant fraction of which is likely to be spent outdoors. Additionally, children routinely spend time outdoors during breaks.
For an initial assessment, it is recommended to assume that a representative child spends a total of 1,250 h y-1 at school, with 1,000 h y-1 of that time spent indoors and 250 h y-1 spent outdoors on school grounds.
3.1.3. Occupancy rates for adults at work
In the UK, a full-time adult worker typically works 1,500 to 2,000 h y-1, depending on factors such as holiday entitlement. For an initial radiological assessment where chronic exposure occurs at work, it is recommended to assume a representative adult works 2,000 h y-1, or 40 hours a week over 50 weeks.
The dose received in the workplace depends not only on the total time worked, but also the type of work environment. For example, an individual working primarily indoors may receive a different dose from an environmental source of radioactivity compared to someone who spends most of their working hours outdoors. It is therefore important to consider the setting and activities required for their role. To support this, occupancy rates are recommended for 2 generic worker types:
Indoor workers are individuals whose primary duties are carried out indoors. For example, office based administrative and clerical roles. A representative indoor worker is assumed to spend 1,800 h y-1 indoors, equivalent to 90% of their annual working hours, and 200 h y-1 outdoors, which accounts for the remaining 10%.
Although some workplaces may be associated mostly with indoor work, it should be considered if there could be roles that require additional time to be spent outdoors. For example, while most schoolteachers will be adequately represented by an indoor worker, a teacher delivering multiple physical education classes on a sports field will spend less time indoors. In the absence of specific information about such workers, a representative individual undertaking this type of work should initially be assumed to follow the occupancy pattern of an outdoor worker.
Outdoor workers are assumed to spend 1,800 h y -1 working outdoors and 200 h y-1 indoors. This is representative of occupations that involve prolonged outdoor activity, such as in agriculture and construction. It is recognised that outdoor workers may work across a relatively large area: for example, a farmer managing dispersed fields. Where appropriate, the total time spent outdoors should be scaled to account for the fraction of time spent within an area where radioactivity is present or could reasonably be expected to be.
Some outdoor work tasks, such as ploughing a field or operating machinery on dry soil, can significantly increase the suspension of dust into the air. While some workers may be in vehicle cabins equipped with air filtration systems, it is reasonable for an initial assessment to assume that these systems have negligible impact on the amount of dust inhaled. The duration of exposure to elevated dust levels can vary considerably; however, a nominal time of 300 h y-1, approximately 15% of the working year, is recommended for initial assessments (21). For simplicity, this time may be applied to any outdoor worker, unless site-specific information indicates a more suitable value should be used.
As the recommended occupancy rates in Table 6 are for chronic exposures, separate typical and high-rate values are not provided. However, it is recognised that some occupations involve highly variable work patterns. For example, farmers may work extended hours during certain periods of the year, such as harvest time. Due to the variability of these working patterns, it is recommended for initial radiological assessments that working hours are evenly distributed throughout the year. This assumption should be reviewed as part of the tiered assessment process if work patterns may overlap with peaks in environmental activity concentrations or after an incident involving mainly short-lived radionuclides.
Table 6. Occupancy rates for members of the public chronically exposed to radioactivity at a location in the terrestrial environment
| Representative person | Age group | Indoor rates (h y-1) | Outdoor rates (h y-1) |
|---|---|---|---|
| Stay-at-home individual | Infants | 7,500 | 500 |
| Children | 7,500 | 500 | |
| Adults | 7,500 | 500 | |
| School | Children | 1,000 | 250 |
| Indoor worker | Adults | 1,800 | 200 |
| Outdoor worker [note 1] | Adults | 200 | 1,800 [note 2] |
Note 1: examples include farmers and construction workers.
Note 2: if required by the assessment, it is recommended that 300 h y-1 of the total outdoor occupancy may be allocated as time spent in enhanced dusty environments, such as during ploughing or operating machinery on dry soil.
3.2. Occupancy rates in aquatic environments
Radioactivity can enter the aquatic environment either directly through liquid discharges, or indirectly via surface run-off which carries radionuclides on land into water bodies. Once in the aquatic environment, radionuclides may remain in the water column or accumulate in sediment, and individuals who spend time in or near the aquatic environment may receive a dose from either source.
Habit surveys conducted around nuclear licensed sites indicate that the main activities undertaken by members of the UK population in aquatic environments include resting, walking, and fishing (22, 23). The frequency of these activities varies by location, individual and season. For example, day-trippers or holiday makers may spend tens of hours a year on a beach in the warmer months, whereas people living in the vicinity may spend hundreds of hours a year walking in the same area, regardless of the weather.
3.2.1 Occupancy rates on beaches and rivers
The recommended typical occupancy rate of 25 h y-1 on a riverbank or beach for all age groups (Table 7) is based on the likely behaviour of a holidaymaker. It is reasonable to assume that children will engage in similar activities to the representative adult, and that infants will be accompanied. Therefore, the recommended exposure time is reasonable for all age groups when used in an initial assessment.
For individuals with higher exposure times, for example, local dog walkers or anglers, an occupancy rate of 1,000 h y-1 is recommended. This represents use of the environment for 2 to 3 hours every day and applies to both adults and children. It should be noted that time spent in the aquatic environment is unlikely to be dedicated to a single activity; rather, it may involve a mix of routine and recreation. As infants are more likely to be present only in periods of good weather, a lower maximum occupancy rate of 100 h y-1 is recommended, representing a few hours a day in the summer months.
Individuals with very high occupancy rates, such as those who live in boats on tidal rivers or who collect molluscs on tidal mudflats, are not accounted for in the recommended rates in Table 7. If such individuals are present or could reasonably be expected to be, site-specific information should be used to define their habits, as the values are likely to be very dependent on local conditions.
Table 7. Recommended occupancy rates for members of the public on a beach or riverbank
| Age group | Typical rate (h y-1) |
High-rate (h y-1) |
|---|---|---|
| Infants | 25 | 100 |
| Children | 25 | 1,000 |
| Adults | 25 | 1,000 |
3.2.2 Occupancy rates for water-based activities
Water-based recreational activities, such as swimming, multisport, paddling, rowing and sailing, may involve full or partial immersion in water, or time spent on the water surface. The recommended occupancy rates for these activities follow the general pattern described previously. Typical values represent individuals such as day-trippers or holidaymakers, who, on average, are expected to spend less time participating in these activities compared to people with more regular access. For typical recreational users of all ages, a nominal occupancy rate of 5 h y-1 is recommended, representing a few visits annually.
Some individuals participate in water-based recreational activities more frequently and for longer durations, with total occupancy rates reaching several hundred hours a year. For adults, a high-rate value of 300 h y-1 is recommended (Table 8), representing active swimmers who swim in open water for approximately one hour on most days. However, this value may not be appropriate for smaller rivers where people are less likely to spend extended time, or where public access is limited.
It is reasonable to assume that children spend less time in water than adults due to environmental and physical constraints, so a reduced high-rate value of 100 h y-1 is recommended for that age group. No high-rate value is recommended for infants as their activities are restricted by safety concerns. Consequently, the nominal occupancy rate of 5 h y-1 should be used for infants in all assessments unless specific information suggests otherwise.
Given the limited data on how time is divided between in-water and on-water activities, initial assessments should cautiously assume the highest potential exposure, either from full immersion in water or exposure on the surface only. This approach should be reviewed as necessary within a tiered assessment framework.
The recommended occupancy rates for recreational water-based activities are intended for members of the public and do not include water sports instructors or other professionals whose values may be significantly higher. Although habits surveys have identified a small number of instructors spending up to 1,000 h y-1 in the water (24), this is considered unusual and not representative of most environments. Instructors should therefore be assessed individually, with consideration given to whether their activities more closely align with outdoor workers.
Table 8. Recommended occupancy rates for recreational water-based activities
| Age group | Typical rate (h y-1) |
High-rate (h y-1) |
|---|---|---|
| Infants | 5 | - |
| Children | 5 | 100 |
| Adults | 5 | 300 |
3.2.3 Comparison of occupancy rates with NRPB-W41
The recommended high-rate values given in Table 7 differ from those previously recommended in NRPB-W41 by standardising occupancy rates across environments and age groups. This includes a reduction by a factor of 2 for adults on a beach and an increase by a factor of 2 to 3 for infants and children on both a beach and a riverbank. These changes are based on a review of recent habits surveys and consideration of behaviour patterns of different age groups. It is also noted that NRPB-W41 did not include recommendations for typical occupancy rates in aquatic environments. These are included in this report, as experience has shown that use of only high-rate values can lead to an overly cautious dose estimate in some circumstances, such as assessing the impact of discharges to remote or difficult-to-access locations.
4. Inadvertent ingestion rates of environmental media
People may inadvertently ingest small amounts of environmental media such as water, soil and sediment, primarily during outdoor activities, and particularly in natural environments. This section presents recommended inadvertent ingestion rates of such media by a representative member of the UK population spending time in terrestrial and aquatic environments.
4.1. Inadvertent ingestion of water
Individuals participating in water-based recreational activities like swimming and other activities may inadvertently ingest small amounts of water, which is a different exposure pathway to the deliberate consumption of drinking water discussed in Section 2.2.
A comprehensive source of information on inadvertent ingestion of water is a report by the US Environmental Protection Agency (EPA) (25). The report reviewed multiple studies and showed that ingestion of water did not vary significantly by location or activity, suggesting that the values would be suitable for use in other countries, including the UK. The EPA recommendations were therefore used to derive recommended inadvertent water ingestion rates for the UK population.
Although only a few studies looked at ingestion of seawater, the EPA review indicated that people inadvertently swallow seawater at similar rates to freshwater, as the mechanisms of ingestion are similar, such as swallowing water while swimming. It is therefore recommended that the same inadvertent ingestion rate is used for both seawater and freshwater.
Based on the EPA review, it is recommended that adults and children inadvertently ingest 50 mL h-1 of water while participating in water-based activities, about 2 mouthfuls for an adult (26). For more cautious assessments, a high rate of 150 mL h-1 can be used.
None of the studies specifically reported inadvertent ingestion rates of water by an infant, so a subjective rate is recommended. As infants are usually accompanied by an adult and are unlikely to spend long periods in water, infants are assumed to have a significantly lower inadvertent ingestion rate compared to children or adults who actively swim. For an initial radiological impact assessment, it is recommended to use 10 mL h-1 as a typical rate and 50 mL h-1 as a high rate for infants.
The recommended inadvertent ingestion rates by a representative infant, child and adult participating in recreational water-based activities are shown in Table 9. The recommended rates represent ingestion of unfiltered water by the representative person and should be applied to the total activity present in the water, including dissolved radionuclides and radionuclides in suspended sediments. Information on recreational water-based activities is given in Section 3.2.
Table 9. Inadvertent ingestion rates of water during recreational water-based activities
| Age group | Typical rates (L h-1) |
High rates (L h-1) |
|---|---|---|
| Infants | 0.01 | 0.05 |
| Children | 0.05 | 0.15 |
| Adults | 0.05 | 0.15 |
4.2 Inadvertent ingestion of soil and sediment
Inadvertent ingestion of environmental media such as soil and sediment can occur through several mechanisms, including eating poorly washed foods, transferring media from hands to the mouth, mouthing by infants, and deliberate ingestion of non-food material due to the pathological condition known as pica. The rate of ingestion can vary greatly depending on individual characteristics, such as age and mental state, and environmental conditions, for example how wet or dry the soil is and how readily material can adhere to skin.
The recommended inadvertent ingestion rates of environmental material for the UK population are presented in Table 10. These rates are based on those suggested by the US EPA (27). Although the studies reviewed by EPA focused on the inadvertent ingestion of soil, for simplicity it is recommended that these rates apply to all types of environmental material, including sand at a beach. US EPA (27) derives inadvertent ingestion rates from time spent outdoors, but since no information was reported specifically for 1-year old infants, the recommended rates are based on the nearest age group with available data (7 months to 4 year olds).
Pica is a rare condition where an individual craves eating non-nutritive items, with soil being one of the most commonly ingested materials (28). The EPA review found that pica behaviour is more common in infants than in children or adults, with occurrence ranging from a one-off event to multiple episodes per week (27). Although relatively few infants exhibit pica behaviour (29), the presence of such behaviour cannot be dismissed within an exposed population. Consequently, the inadvertent ingestion rate of soil by a representative infant should account for this. The EPA reported that the typical rate of soil ingestion by infants during non-pica behaviour, was 18 mg h-1. To account for some limited pica behaviour throughout the year, the recommended typical inadvertent ingestion rate of soil by a representative infant was rounded to 20 mg h-1.
To account for the possible presence of an infant who exhibits significant pica behaviour, a high-rate of inadvertent ingestion of soil of 850 mg h-1 is recommended (30, 31), noting that the mass of material ingested during periods of significant pica behaviour will substantially exceed that ingested during other times. This value should be used together with the number of hours when pica behaviour is found to occur.
When applying the rates given in Table 10, it is important to consider the type of environment in which the exposure occurs. In settings where above average ingestion of soil is likely to occur, such as muddy areas or sandy beaches, an assessment should consider using high rates. Where inadvertent ingestion of environmental media is minimal, for example grassed or paved areas, typical rates would be more appropriate.
Table 10. Inadvertent ingestion rates of environmental media including soil and sediment
| Age group | Typical rates (mg h-1) |
High rates (mg h-1) |
|---|---|---|
| Infants [note 1] | 20 | 850 |
| Children | 15 | 40 |
| Adults | 5 | 35 |
Note 1: includes a contribution from pica behaviour.
4.2.1. Comparison of inadvertent ingestion rates with NRPB-W41
Although the typical inadvertent ingestion rates of environmental media in Table 10 are generally the same or lower than those recommended in NRPB-W41, there is a significant increase in the high-rate value for infants. The recommended high-rate value for this age group has increased by a factor of more than 3 due to the inclusion of pica behaviour. However, as most time spent outdoors is expected to be associated with typical rather than high rates of inadvertent ingestion, the overall impact of these changes is expected to be low in most situations. An exception is recreational use of beach environments, where the potential for high-rate ingestion may continue throughout the time spent in such environments.
5. Inhalation rates
Inhalation of radionuclides present in air is a significant exposure pathway (32), and assessing the radiation dose from this pathway requires data on inhalation rates. The Human Respiratory Tract Model (HRTM), described by ICRP in Publication 66 (33), is a reference biokinetic model used to calculate dose coefficients from the inhalation of airborne radionuclides. In the publication, ICRP presented data on respiratory rates for different population groups, which were subsequently reviewed and republished as reference values in ICRP Publication 89 (34). These rates were used to derive the recommended inhalation rates published in NRPB-W41.
Although ICRP has made some changes to the HRTM (35), the recommended inhalation rates have not changed, so the recommended rates published in NRPB-W41 remain the most appropriate values to use in radiological impact assessments. ICRP presented inhalation rates for males and females, but the recommended rates are those of males as they are up to 50% higher than the equivalent female values so their use provides a suitable level of conservatism in an assessment.
5.1. Inhalation rates for members of the public
ICRP Publication 89 presents reference inhalation rates for different ages and activities, including sleeping, sitting, and engaging in light or heavy exercise (34). Light exercise includes walking or cleaning, while heavy exercise includes playing sports, digging, or other activities where inhalation rates will be significantly above normal. Given the types of activities that heavy exercise is intended to represent, ICRP recommends that this rate is limited to 2 hours in any 24-hour period. These reference inhalation rates are given in Table 11.
Table 11. Inhalation rates for representative members of the public during acute exposures to airborne radioactivity
| Age group | Sleeping (m3 h-1) |
Sitting m3 h-1) |
Light exercise (m3 h-1) |
Heavy exercise [note 1] (m3 h-1) |
|---|---|---|---|---|
| Infants | 0.15 | 0.22 | 0.35 | - |
| Children | 0.31 | 0.38 | 1.10 | 2.20 |
| Adults | 0.45 | 0.54 | 1.50 | 3.00 |
Note 1: not to be used for more than 2 hours per day.
For members of the public, the recommended hourly and annual inhalation rates for use in situations of chronic exposure to airborne radioactivity are presented in Table 12. These rates were derived by scaling the rates in Table 11 to the time an individual participates in each of the activities. The times used in this calculation were from ICRP Publication 89 (34), and are also shown in Table 12.
Table 12. Inhalation rates for representative members of the public during chronic exposure to airborne radioactivity
| Age group | Hourly inhalation rate (m3 h-1) |
Annual inhalation rate (m3 y-1) |
|---|---|---|
| Infants [note 1] |
0.22 | 1,900 |
| Children [note 2] |
0.64 | 5,600 |
| Adults [note 3] |
0.92 | 8,100 |
Note 1: rates based on 14 hours of sleeping (0.15 m3 h-1) and 10 hours of play time (0.31 m3 h-1 based on 1/3 sitting (0.22 m3 h-1) and 2/3 light exercise (0.35 m3 h-1)).
Note 2: rates based on 10 hours of sleeping (0.31 m3 h-1) and 14 hours of play time (0.87m3 h-1 based on 1/3 sitting (0.38 m3 h-1) and 2/3 light exercise (1.10 m3 h-1)).
Note 3: rates based on 8.5 hours of sleeping (0.45 m3 h-1), 13.5 hours of housework or miscellaneous (1.18 m3 h-1 based on 1/3 sitting (0.54 m3 h-1) plus 2/3 light exercise (1.5 m3 h-1)), and 2 hours of outdoor activity (1.21 m3 h-1 based on ½ sitting (0.54 m3 h-1) plus 3/8 light exercise (1.5 m3 h-1) plus 1/8 heavy exercise (3 m3 h-1)).
5.2. Inhalation rates for members of the public exposed at work
In some assessments, the representative person may be exposed to airborne radioactivity only during time spent at work. For example, when radioactive dusts present in the work environment are resuspended by wind or mechanical activity, a person working in that area may inhale that radioactivity during their workday. These scenarios may involve people in physically active roles like construction workers who undertake high levels of manual labour or more sedentary roles such as machinery operators or desk-based workers. It is noted that, unless the individual is specifically employed to work with radioactivity, all those exposed at work should be radiologically assessed as being a member of the public.
The recommended inhalation rates for both sedentary and active workers are given in Table 13 together with the assumptions used in their derivation, which are based on guidance in ICRP Publication 66 (33). The inhalation rates given in Table 13 are the same as those previously recommended in NRPB W41.
Table 13. Inhalation rates for representative members of the public during chronic exposure to airborne radioactivity when at work
| Age group | Hourly inhalation rate (m3 h-1) | Annual inhalation rate (m3 y-1) [note 1] |
|---|---|---|
| Adult (sedentary worker) [note 2] |
1.2 | 2,400 |
| Adult (active worker) [note 3] |
1.7 | 3,400 |
Note 1: rates based on a 2,000 hour working year.
Note 2: rates based on an individual spending 2.5 hours sitting and 5.5 hours doing light exercise over a working day.
Note 3: rates based on an individual spending 7 hours doing light exercise and 1 hour doing heavy exercise over a working day.
6. Conclusions
This report provides updated recommendations for defining the habits of a representative member of the public when assessing potential exposure to radioactivity. It replaces the previous guidance published in NRPB-W41 (1). The recommended values include how much food and water people consume, breathing rates, inadvertent ingestion rates of environmental media, and occupancy rates for locations that are commonly included in radiological impact assessments. This information is provided for 3 age groups: 1 year olds, 10 year olds and adults, based on the ICRP recommendations on defining the representative person.
Generally, the recommended habits are similar to those previously recommended in NRPB-W41, with most differences being within a factor of 2. Where there are differences, these are mainly due to the availability of more recent or comprehensive data. In addition to providing updated values for use in radiological assessments, this report provides guidance on the use of such values. It highlights that use of the recommended habits assumes that the representative person has habits similar to that seen in the wider UK population. As such, the recommended habits are intended to be used to estimate the initial dose in a tiered assessment process, supplementing rather than replacing any site-specific information. This can be especially useful when performing a prospective assessment to understand the impact of any reasonably foreseeable changes in people’s habits on the dose received. However, using generic habits can introduce uncertainty, so the impact of using such data should be reviewed as necessary as part of the tiered assessment process.
Acknowledgements
The authors wish to acknowledge the support given to them by the Food Standards Agency with regards to analysing data collected within the NDNS and DNSIYC surveys.
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