Guidance

Crematoria: process, types of fuels and flue gas treatment

Published 4 December 2025

This document is part of the crematoria technical guidance. There are 4 more documents that cover this topic.

Read all the documents to make sure you have the information you need.

Cremation process  

Cremators comprise a primary and a secondary combustion chamber. Both chambers have a refractory lining to retain heat and to protect temperature sensitive equipment. The coffin containing the deceased is placed into the primary chamber through a doorway at one end of the primary chamber. Loading can be done manually or may be partly automated. 

In current gas-fired cremators, there is usually a single burner installed within the primary chamber which directs a flame at the coffin. Cremators can have more than one burner in a range of configurations. The direction of the flame can be controlled to a limited extent by adjusting the injection of the combustion air. 

As the fuels used diversify, a key technology will be burners which can utilise a range of different fuels, such as biofuels, hydrogen and natural gas or hydrogen blends. 

In electric cremators, there are a number of adjustable electrical heating elements (typically 6), which indirectly heats the primary chamber to above the auto-ignition temperature. No additional fuel is added but air must be added to sustain combustion. 

Timings and steps 

Cremation is a batch process consisting of (excluding pre-heating and shutdown) the steps shown in Table 1. 

Indicative timings for existing gas cremators are shown in table 1. Total cremation times may vary considerably, ranging from as little as 50 minutes to more than 2 hours, depending upon body size. 

Cremation times on recently installed electric cremators are longer, but there is insufficient data to make a direct comparison. 

Table 1: Steps in the cremation process 

Process step	Typical time required (gas cremators)
Brief “flash” caused by volatilisation of the veneer on the outside of the coffin	1 minute
Burning of the coffin	20 minutes
After the coffin breaks open, burning of the coffin and cremation of the body	40 minutes
Calcination of the remains (when there are no flames from the remains at the end of the cremation)	30 minutes
Ashing	2 minutes although times may vary

Using the secondary combustion chamber 

The purpose of the secondary combustion chamber is to provide sufficient temperature and residence time for the complete oxidation of all the gaseous products of combustion in the primary chamber.  

In gas cremators, typically a single supplementary burner is installed to maintain the temperature of the secondary chamber if needed, although cremators can have more than one secondary burner. In electric cremators, electrical heating elements are used.  

In both cases, the retained heat from the primary combustion chamber is often sufficient to maintain temperature. Supplementary air is added to ensure there is sufficient oxygen present to complete the combustion process. 

Raking ashes after cremation  

The raking of the ashes into a suitable container can be from either end of the primary chamber based on the design. The remains are then taken to a cremulator where they are processed for return to the family of the deceased.  

Using cremulators 

Cremulators are compact pieces of equipment fitted with a small filter which can vent internally or externally to the building. Care is needed when moving the remains from the primary chamber to the cremulator to avoid generating dust. 

Types of fuels used in cremators 

The majority of cremators currently in operation in the UK are fuelled using gas, either natural gas or liquefied petroleum gas (LPG). There are only a few cremators which can use both gas and liquid fuels. Some temporary cremators use only liquid fuels. There are a small number of electric cremators, which with one exception have been installed during the past 3 years. 

There is a growing focus on the more efficient use of existing fuels, the use of new fuels such biogas, hydrogen and liquid biofuels and their environmental impacts. The composition of natural gas could also change with the addition of up to 20% hydrogen into the supply network. 

The recent increase in electric cremators is partly motivated by the reducing carbon intensity of the electricity network and it is expected that more will be installed in the next few years. 

In the future, cremators will likely use a more diverse range of fuels and so where reference is made in this guidance to new crematoria, this applies to all new cremators regardless of fuel type. Where reference is made to existing crematoria, this applies to gas fired and electric cremators currently in operation. 

Types of cremators

In this guidance a: 

• new cremator is one that first comes into operation 1 month after publication  
• existing cremator is one that is not a new cremator   

Standby cremators 

A standby cremator is one that is permanently retained for use in the event of breakdown of the main cremators or other occasional need (excluding small-scale cremators) for additional cremator capacity at the crematoria.  

Standby cremators, which are not fitted or connected to flue gas treatment, shall operate for no more than 100 hours in any calendar year. In general, standby cremators should meet all the standards which apply to unabated cremators. This is described in more detail later in the guidance. 

Standby cremators may be brought into operation subject to the following conditions: 

• the standby cremator must be included in the environmental permit and be clearly identified 
• the regulator must be notified, in advance where possible, of the operation of the standby cremator 
• the standby cremator shall not be brought into operation unless there is a clear operational need - all periods of operation and the reason for standby cremator operation must be recorded in the log 
• standby cremators, which are not fitted with or connected to flue gas treatment equipment, shall operate for no more than 100 hours in any calendar year - meaning a cremation must not be started once 100 hours have elapsed 
• the number of hours operating standby cremators shall be reported to the regulator 

The calculation of 100 operational hours shall exclude periods of pre-heat prior to the start of operation, and any period needed to complete a cremation begun before the 100-hour operational limit has been reached. However, it will include the period between successive cremations carried out on the same day.  

In addition: 

• the operator shall make visual and olfactory assessments of emissions at the start and at least once during each cremation cycle - the location and result of the assessment shall be recorded in the log  
• if a standby cremator is in operation when emissions testing takes place, the emissions testing will include the standby cremator  

Emissions testing shall not be rescheduled or postponed just because the standby cremator is in operation. Emissions to air from the standby cremator shall not exceed any of the relevant emission limit values. 

In all other respects, standby cremators must meet the requirements set out in this guidance. Specifically, standby cremators must comply with the operational controls described in the guidance document for crematoria: emissions limits, monitoring and other provisions. The operational controls are for: 

• temperature in the secondary combustion chamber  
• oxygen and carbon monoxide at the exit of the secondary combustion chamber 

The term standby cremator is not to be confused with a temporary cremator. 

Temporary cremators 

A temporary cremator is a cremator installed on a temporary basis usually as a replacement for one that has been taken out of service for replacement or major refurbishment.   

Where an unabated temporary cremator, replaces a cremator with flue gas treatment and is required to operate for more than 100 hours, an assessment of the impact on local ambient air quality shall be made as part of the permit variation application. Guidance on assessing the impact of your emissions to air is included in the document for crematoria: emissions limits, monitoring, and other provisions. 

From 1 month after publication, if the temporary cremator is installed as additional capacity or is intended to be in service for more than one calendar year, it shall meet the standards for new cremators. 

Not all the standards for full scale cremators are appropriate for small-scale cremators because of the relatively small mass of pollutants emitted. 

Small-scale cremators 

A small-scale cremator is one that is retained specifically to cremate stillbirth, neonatal and foetal remains. Small-scale cremators will have a door opening which is a maximum of 300mm by 300mm and the primary chamber will be no more than 1,000mm long.  

Some of the requirements of this guidance are not appropriate for such small-scale cremators because of the relatively small mass of pollutants emitted, and the like absence of mercury. For example: 

• small-scale cremators are not required to fit flue gas treatment 
• emission limit values for emissions to air do not apply to small-scale cremators 
• emissions monitoring of small-scale cremators is not required 

In all other respects, small-scale cremators must meet the requirements set out in this guidance. Specifically, the small-scale cremator must comply with the operational controls described in the guidance document for crematoria: emissions limits, monitoring, and other provisions.  

Where the small-scale cremator is a standalone facility (meaning it is not part of an otherwise regulated facility) emissions may be considered trivial and with the agreement of the regulator, will not require a permit.  

When stillbirth, neonatal or foetal remains are cremated in other types of cremators (including standby cremators), the guidance for those cremators will still apply. However, because of the shorter cremation times, it is not recommended to carry out emissions monitoring during such cremations. 

Flue gas treatment  

In 2023, approximately 70% of cremations in the UK were carried out in cremators fitted with a flue gas treatment system. 

Flue gas treatment was originally introduced to reduce emissions to air of mercury, which arise from dental amalgam. However, the flue gas treatment system is also effective at reducing emissions of dust (particulate matter), acid gases and dioxins. 

The principle of the system is the injection of reagents into the flue gas, usually a mixture of sodium bicarbonate or lime and activated carbon. The sodium bicarbonate or lime reacts with the acidic gases and the carbon absorbs mercury and dioxins. The spent reagent is then filtered out of the air stream using a bag or ceramic filter. 

Using a different design, the flue gas first passes through a bag or ceramic filter to remove particulates and then the filtered gases pass through a fixed bed of sodium bicarbonate or lime and activated carbon to remove acid gases, mercury and dioxins. In this system, the reagents in the fixed bed need to be replaced before they become fully spent or saturated. 

Both these forms of flue gas treatment require the combustion gases first to be cooled. This need to cool the exhaust gases is an opportunity to recover heat, usually in the form of hot water, such as for use in heating buildings. 

Flue gas treatment is commonly referred to in the industry simply as ‘abatement’. Cremators without flue gas treatment are referred to as ‘unabated cremators’. 

Abatement of nitrogen oxides (NOx) 

However, flue gas treatment does not remove nitrogen oxides (NOX). More recently, some equipment providers have started to provide a NOX abatement option using a process of selective non-catalytic reduction (SNCR). The use of this technique is currently quite limited but is becoming more widespread. This is referred to as ‘NOX abatement’ or ‘SNCR’.

This document is part of the crematoria technical guidance.

Next: Crematoria: emissions limits, monitoring and other provisions.