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Emissions from Spoil Pile Fires

Open Cut » Health and Safety

Published: January 99Project Number: C4014

Get ReportAuthor: John Carras, S Day, AL Lange, PF Nelson, DB Roberts, F Szemes, A Tibbett, DJ Williams | CSIRO Energy Technology

The project arose from considerations of the possible effects of the emissions from spontaneous combustion in spoil piles on the occupational health and safety of mine workers. Fires from spontaneous combustion can be associated with open cut and underground coal mining.  This is because coal reacts with atmospheric oxygen to liberate heat.  This heat may accumulate, resulting in temperature rises which can lead to ignition.  Open cut coal mining produces spoil piles which consist of overburden, partings, unrecovered coal and carbonaceous shales, siltstones and mudstones.  The carbon content of many of the materials renders them liable to spontaneous combustion with consequent emissions of heat, particles and gases.

The emissions from incomplete coal combustion are known to contain chemical compounds which may be harmful to human health if present in sufficient concentrations or exposures.  These include sulphur dioxide, carbon monoxide, methane and the heavier hydrocarbons typically associated with coke oven emissions. 

The objective of the project was to measure the concentration and exposures that might be experienced by mine workers due to selected organic air toxics arising from the emissions from spontaneous combustion in open cut coal mining.

The objective was to be achieved by a program of field sampling with subsequent chemical analysis of the samples in CSIRO North Ryde Laboratories. 

The work program required the development of a sampling package which was fitted to a specially modified D11 bulldozer.  A program of field sampling for polynuclear aromatic hydrocarbons (PAH) within the cabin of the dozer, was carried out.

A total of 26 different sampling periods were obtained as required by the work program.  The report presents a  detailed description of the method employed during the project and the results obtained.

PAH - Polynuclear Aromatic Hydrocarbons

The United States Environmental Protection Agency (USEPA) has identified and listed a number of chemical compounds which are known to be important for human health.  Some of these compounds have been classified as air toxics, for which the USEPA intend to introduce air quality standards.  Among the compounds included as air toxics are polynuclear aromatic hydrocarbons (PAHs).  These compounds result from partial combustion.  The carcinogenic effect of some of these compounds has been established.  However, not all PAHs are carcinogens. 

PAHs are found in a number of workplaces.  For instance petroleum, coke making, anode production and aluminium production may involve occupational exposures to PAHs.  Processes associated with coal tar, pitch, asphalt, creosote, soot, anthracene and engine exhausts can also result in occupational exposures to PAHs.

The USEPA has proposed regulations for governing major sources of PAHs and has developed reference doses for some PAHs.  However no reference concentrations exist for any PAHs.  In Australia two types of PAHs, (benzo(a)pyrene and chrysene) are specifically referred to in the National Occupational Health and Safety Commission’s National Exposure Database, but no exposure limits have been set.  Instead, they recommend that exposure to these compounds be controlled to the lowest practicable limit.

Experimental Method

The approach adopted in this study was to determine the exposure of a typical worker while performing normal duties driving heavy machinery (e.g. a bulldozer) on the mine.  The vehicle chosen for the study was a Caterpillar D11 bulldozer.  The cabin was modified so that a sampling line could pass into the bulldozer cabin from the sampling package which was mounted external to the cabin.

The standard method for collecting PAHs is to capture the particle matter on a clean polyurethane foam filter.  After sampling, the filter was analysed in the laboratory for PAHs.  However in order to sample PAHs in the field a special sampling package had to constructed.  The package had to be small enough to be be located aboard the field vehicle as well as sufficiently rugged to withstand the rigors of bulldozer operation.

Samples were taken from the bulldozer cabin as well as from various stationary points around the mine site.  Samples were collected continuously for about eight hours.

Project Findings

In general the results of the cabin air were lower than those observed for the outdoor samples from stationary locations.  For each sample, the total concentration of PAHs was at the low end of the concentration which might be expected for urban air.  The air samples taken from outdoor stationary locations were higher, and in some cases much higher, than the cabin air.  However, for stationary samples, the sample package was usually placed fairly close to regions of spontaneous combustion (for example in the middle of a hot spot in windy conditions).

The highest data for the open air samples suggest that workers working outside in close proximity to spontaneous combustion fires, may experience exposures that are higher than the recommended occupational health and safety values.

For the sampling periods undertaken in this study, the data showed that the air within the bulldozer cabin is relatively low in PAH concentrations and is within the recommended occupational health and safety guidelines.

The major finding of the project is that the exposures to PAHs, measured within the cabin of a bulldozer operating at a coal mine with spontaneous combustion in the spoil piles, were shown to be below the values expressed by the occupational health and safety guidelines.  In outside air and in close proximity to spontaneous combustion fires PAH levels may be sufficiently high to result in exposures which may be greater than the recommended values.

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