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(Adapted from the Rhode Island Committee on Occupational Safety and Health)
Diesel fuel powers lots of equipment and vehicles. Examples include backhoes, loaders, cranes, trucks, buses, forklifts, generators, tractors, pumps, fire trucks. Diesel exhaust is made up of two types of materials: gases and particulates (soot). Carbon monoxide, nitrogen oxides, phenol, formaldehyde and PAHs (polynuclear aromatic hydrocarbons) are some gases in diesel exhaust. Diesel exhaust is also composed of very small particles and clumps of particles (the soot part). Chemicals in the gas part will hitch a ride on the surface of these particles. As you breathe in particles – and you can breathe a lot of them deep into the lungs – these chemicals go along for the ride.
The composition and distribution of all these compounds vary by engine type, driving technique, air/fuel ratio, vehicle load, and temperature and fuel type.
Health Effects of Diesel Exhaust
- Diesel exhaust causes irritation of the respiratory tract, which may result in changes in lung function – usually reversible.
- Medical experts are concerned that diesel exhaust can aggravate preexisting lung disease such as asthma and heart disease.
- Medical authorities suspect that diesel exhaust may increase the risk of lung cancer. Diesel exhaust is under suspicion because animal studies have shown such. And, many chemicals that are found in diesel exhaust – PAHs are one set – are known or strongly suspected to cause cancer. If the exposure is in the general environment the increase is likely to be very slight. Risk is higher in environments where exposure is prolonged and heavy.
- Diesel exhaust levels should be measured especially when working near diesel equipment or vehicles in enclosed spaces. But, diesel exhaust is not something that can be measured directly. What technicians do is choose among several compounds that are in diesel exhaust and use that compound as a surrogate for the whole. (Since many of these same compounds come from other sources besides diesel exhaust, a technician needs to be aware of cross contaminations when they monitor.)
- Some compounds chosen as surrogates are: 1] Total particulates, 2] Elemental carbon,3] PAHs (benzene solubles, solvent solubles, coal tar pitch volatiles) 4] Carbon Monoxide
- If either elemental carbon or total particulates is chosen then an air-sampling pump with a filter can be used. A more expensive device, which gives a direct read over a period of time so that you may detect peaks, is also available. To measure PAHs you need an air-sampling pump with charcoal tubes. For carbon monoxide either a carbon monoxide meter or a hand-held detector tube pump with carbon monoxide tubes can be used.
- The preferred gold standard used by OSHA/NIOSH: select carbon and measure using a sampling pump with 37 mm quartz fiber filter 2-4liter flow rate.
CDC’s National Institute for Occupational Safety and Health has concluded:The excess of cancer risk for workers exposed to diesel exhaust has not yet been quantified, but the probability of developing cancer should be decreased by minimizing exposure. As prudent public health policy, employers should assess the conditions under which workers may be exposed to diesel exhaust and reduce exposures to the lowest feasible limits.
Measuring Diesel Exhaust
There are no federal occupational health standards for diesel exhaust. There is a voluntary guideline published by a professional association of industrial hygienists (ACGIH). They propose an exposure limit of diesel exhaust of .2mg/.3mg (using elemental carbon as the measuring rod).Federal clean air (environmental) rules mandate much cleaner diesel exhaust standards.
Methods to Control Diesel Exposure
- The composition of diesel exhaust can vary with fuel type; consequently fuel modifications can be effective in reducing diesel emissions. Ultra low sulphur fuels are recommended: sulphur content of the grade of diesel fuel should less than .10%( point ten percent) or 15ppm( parts per million) or lower.
- Proper engine maintenance, especially with better grade diesel fuel, plays a significant role in lowering diesel exhaust.
- Diesel exhaust can be vented directly to the outside of a working space, that is away from workers breathing zones. This involves attaching a flexible tube to a vehicle’s exhaust pipe that vents directly out of an enclosed space like a bus barn or fire station. Exhaust vents should be away from windows and fresh air intakes.
- In enclosed work areas (tunnels, warehouses) equipment modifications are used. These include particle traps, catalytic converters, high efficiency filter devices.
- Evaluate alternative equipment and alternative vehicles. Many transit authorities now purchase buses fueled by compressed natural gas. Many industries choose electrical or propane forklifts. Propane forklifts generate higher levels of carbon monoxide than diesel so if a substituted vehicle is used indoors then other hazards may be a problem and need to be addressed and controlled.