High dioxin emissions measured at crematoria

Some of the highest emissions of dioxins and furans measured in the UK have been detected at two crematoria during tests carried out by Warren Spring Laboratory (WSL).1 The study has also suggested that existing crematoria may have grave difficulties in meeting tighter emission standards due to be phased in over the next five years.

WSL's study was commissioned by the Department of the Environment (DoE) shortly after emission controls for crematoria were introduced under the Environmental Protection Act 1990.

Enforced by local authorities, the rules require all existing crematoria to be upgraded to emission standards set for new plant by April 1998. About 240 crematoria are currently operating in Britain, and all but 15% are run by local authorities.

Very few data are available on emissions from crematoria, and WSL's study was a first attempt to build up the body of evidence. Tests were carried out at two plants. One was a manually operated process with two units designed to burn one coffin at a time. The second was of a similar design, but had been modified in an attempt to bring it into line with the new plant standards. The modifications included computer control of the combustion process, uprated burners, and improved secondary combustion facilities designed to ensure that flue gases are maintained at 850°C for two seconds. Neither plant had any flue gas cleaning equipment.

The main results are summarised in the table, and are compared with the limits set for new plant in a DoE guidance note.

The results showed considerable variability in emission levels, even from the same plant. However, they suggest that even the modified unit would need abatement equipment to ensure consistent compliance with the limits for particulates and hydrogen chloride, while the unmodified unit would clearly struggle to meet all of the new plant limits.

Dioxin and furan emissions, expressed as the equivalent (TEQ) in terms of toxicity to the most toxic dioxin isomer, 2,3,7,8-TCDD, were towards the high end of values recorded by WSL and others in investigations at British municipal waste and clinical waste incinerators in recent years (ENDS Reports 195, pp 13-14, and 196, pp 10-11). They were also well above the limit of 1ng/m3 set by the guidance note for plants which do not have secondary combustion facilities capable of maintaining flue gases at 850°C for at least two seconds.

The study identified enough grounds for concern for WSL to recommend further investigations at other crematoria. However, although it was completed early in 1992, no further work has yet been commissioned by the DoE.

The report poses two important questions for the DoE. If the results are indicative of emissions from other crematoria, they suggest either that costly acid gas and particulate abatement equipment will be necessary even on improved combustion units, and even though this is something that the DoE had not bargained for when setting the new plant limits. Alternatively, it could relax the limits. Indeed, last year the DoE doubled the original 100mg/m3 limit for hydrogen chloride after it became clear that it would be difficult to meet without add-on abatement equipment - but clearly this is something which cannot be done too often without damaging the credibility of the new regime.

Secondly, WSL's work has made it plain that even a unit meeting the minimum secondary combustion requirements of a two-second flue gas residence time and a temperature of 850°C will not on its own reduce dioxin and furan emissions to anything like 1ng/m3 - yet the existing guidance allows operators complying with those requirements not to take any other measures to control these pollutants.

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