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RAF weatherman Sergeant Karl Rhodes explains why temperature measurements are such a burning issue in Defence.
Temperature information is hugely important to personnel who have not properly acclimatised to their new overseas location, such as the Middle Eastern air base of 902 Expeditionary Air Wing where Sergeant Rhodes is currently deployed.
RAF personnel have to work outside in some fairly harsh conditions, much hotter than in the UK, and very often they’re doing this for long periods. I measure the temperature outside several times a day and warn of the risks to those working.
Service personnel can be exposed to many forms of heat illness caused by not only high temperatures, but also by a range of combining factors including high intensity activity and the heat stress caused by the wearing of Personal Protective Equipment (PPE) such as body armour and helmets, with flight line PPE or the specialist PPE worn by firefighters having the the worst adverse effects.
In hot environments heat loss is mainly by evaporation of sweat, although a small amount will be lost by conduction and convection, so cooling down in ‘hot and sticky’ conditions of high humidity is much harder. Sergeant Rhodes said:
The average high temperature for here is 39 degrees C in June, but never falls much below 27 degrees C throughout the rest of the year.
Humidity is the real difficulty,” he continued. “77 per cent in August and never below 45 per cent for the rest of the year. In comparison, the UK highest average temperature is 23 degrees and humidity is not even routinely mentioned.
Being able to predict the effects of the temperature is vital for local commanders to moderate the work rate of individuals, to understand the rate that personnel can cool down, and encourage, or even enforce, regular rehydration.
Cooling is determined by the temperature, humidity and wind speed. These factors can be integrated into an index of environmental temperature. According to Sergeant Rhodes the index most suitable for military use is the Wet Bulb Globe Temperature (WGBT) Index. He explained:
The WBGT device used by the RAF, and the rest of the military, is a Quest Temp 34. It’s a rugged thermometer which calculates the heat index by taking three different temperature readings using a wet bulb to measure evaporation, a dry bulb for normal air temperature, and a globe for solar radiation.
These temperatures are then combined in the machine to give a Heat Index number. This he records throughout the working day at two- to four-hourly intervals and prominently displays the readings in the operations control room and other communal areas such as the mess for the benefit of all.
Published: 12 April 2011
From: Ministry of Defence