Control measures for diesel engine exhaust emissions in the work place

From Employment and Social Development Canada

This guideline has been developed by the Labour Program to assist federally regulated workplace parties understand how to manage and control exposure to diesel engine exhaust emissions (DEEEs) in the work place, and for identifying in which work places this hazard is commonly found. The Guideline will be particularly useful for industrial hygiene specialists and health and safety professionals who may be recommending or installing different control measures that are appropriate for federal jurisdiction legislative and meet regulatory requirements.

1. Introduction

The lean-burning nature of diesel engines and the high temperatures and pressures of the combustion process result in significant production of nitrogen oxides, and provide a unique challenge in reducing these compounds. Modern on-road diesel engines typically use selective non-catalytic reduction to meet emissions laws, as other methods such as exhaust gas recirculation cannot adequately reduce nitrogen oxides to meet newer standards in many jurisdictions. However, the fine particulate matter in the exhaust emissions (sometimes visible as opaque dark-coloured smoke) has traditionally been of greater concern, as it presents different health concerns and is rarely produced in significant quantities by spart-ignition engines. It was reported in 2012 that although total nitrogen oxides from petrol/gasoline cars have decreased by around 96% through adoption of exhaust catalyst, diesel cars still produce nitrogen oxides at a similar level to those bought a decade and a half ago under real world tests, resulting in diesel cars emit around 20 times more nitrogen oxides than petrol/gasoline cars^{Footnote 1}.

In addition to nitrogen oxides, diesel engines produce carbon (soot), sulphur oxides, for example, sulphur dioxide, aldehydes, ketones, alcohols, nitrogen, hydrocarbons, polycyclic aromatic hydrocarbons and water. Diesel engines produce very little carbon monoxide as they burn the fuel in excess air even at full load.

The quantity and composition of diesel engine exhaust emissions vary depending on:

• the type of engine
• the composition of the fuel
• maintenance and tuning
• the engine temperature
• the workload

There are also three types of visible smoke that may be produced during the diesel fuel combustion process. White smoke (water droplets and unburnt fuel) is observed when the engine is started from cold. Blue smoke (oil and unburnt fuel) is associated with poorly serviced and tuned engines, and black smoke (soot, oil and unburnt fuel) indicates mechanical problems. The soot content varies from 60% to 80% depending on the fuel used and condition of engine^{Footnote 2}.

2. Occupational exposure to diesel engine exhaust emissions

Worker exposure to diesel exhaust mainly occurs by breathing in the gases and soot, which then enter the workers’ lungs. Repeated exposure to diesel exhaust can lead to lung and bladder cancer and can also cause chronic bronchitis, chronic obstructive pulmonary disease and asthma. According to Carex Canada, 897,000 Canadian workers face exposure to diesel exhaust at work every year^{Footnote 3}.

The major sources of worker exposure to diesel exhaust are from heavy vehicles that use diesel fuel such as trucks, trains/locomotives, buses and fork-lift trucks. As a result, employees in the following types of work places are among the most affected in the federal jurisdiction:

• inter-provincial trucking, vehicle maintenance and repairs
• railways, railway repairs and rail tunnels^{Footnote 4}
• bus garages, vehicle maintenance and repairs
• toll booths, warehouses and garages
• airport ground service equipment and auxiliary, luggage transport service

3. Federal legislation requirements

Part X (hazardous substances) of the Canada Occupational Health and Safety Regulations^{Footnote 5} issued under Part II of the Canada Labour Code requires that, if there is a likelihood that the health or safety of an employee in a work place is or may be endangered by exposure to hazardous substances (including diesel engine exhaust emissions), a hazard investigation to assess the risks to health must be conducted. On completion of the investigation, it is further required that employee exposure to the hazardous substance be eliminated or reduced by the implementation of engineering controls and, if necessary, other control measures such as administrative controls and the use of respiratory protection devices. The adequate maintenance of the controls that have been implemented, as well as employee training, are also required.

4. Occupational exposure limit

The Regulations prescribe the occupational exposure limits for hazardous substances. Subsection 10.19(1)(a) states that an employee shall be free from exposure to a concentration of an airborne chemical agent in excess of the value for that chemical agent adopted by the American Conference of Governmental Industrial Hygienists in its publication entitled Threshold Limit Values and Biological Exposure Indices^{Footnote 6}.

However, due to disagreement among experts on what components of diesel exhaust should be measured to accurately assess exposure, the American Conference of Governmental Industrial Hygienists offers no specific Threshold limit value for diesel engine exhaust emissions.

In 2012, the International Agency for Research on Cancer, which is part of the World Health Organization, classified diesel engine exhaust emissions as carcinogenic to humans (Group 1), based on sufficient evidence that exposure is associated with an increased risk for lung cancer and limited evidence with an increased risk for bladder cancer^{Footnote 7}.

It is a general rule that exposures to carcinogens must be kept to a minimum. Employees who are or may be exposed to confirmed human carcinogens without a Threshold Limit Value or occupational exposure limit should be properly equipped to eliminate or, if not reasonably practicable, to reduce to the fullest extent possible all exposure to the carcinogen.

5. Control measures

Measures to mitigate exposure to diesel engine exhaust emissions include:

• modifying the engine
• installing diesel particulate filters
• implementing exhaust gas recirculation
• selective non-catalytic reduction
• using other fuels, such as dimethyl ether or low sulfur diesel
• proper maintenance of the engine and exhaust system

An excellent source of information is the Health and Safety Executive publication entitled Control of diesel engine exhaust emissions in the workplace^{Footnote 2}.

The publication identifies warehouses, depots, and bus garages as work places where diesel engine exhaust emissions are common occupational exposures. Examples of good working practices for controlling the engine exhaust emissions from diesel powered vehicles such as fork-lift trucks, railway locomotives, buses and lorries, and where there is likely to be an accumulation of diesel exhaust such as in warehouses, locomotive depots, bus garages, vehicle testing sites, fire stations etc. are provided. Many methods also apply to emissions from petrol/gasoline engines.

Substituting diesel fuel with a safer fuel, for example, dimethyl ether or low sulphur diesel fuel, or alternative technology, for example, battery operated vehicles or equipment would be the most effective way to reduce exposure, however, in many instances, these solutions neither are reasonably practicable nor possible, and other options or a combination of options should apply.

The three most effective engineering controls to eliminate or reduce exposure to diesel exhaust are the use of:

• engine exhaust filters
• local tailpipe exhaust ventilation
• dilution ventilation

In addition, administrative controls^{Footnote 8} such as:

• modifying the methods of work, for example, by limiting speeds and using one-way travel routes to minimize traffic congestion or prohibiting and/or restricting unnecessary idling or lugging of engines;
• modifying the operations, for example, by restricting the amount of diesel-powered equipment and total engine horsepower operating in a given area and ensure that the number of vehicles operating in an area does not exceed the capacity of the ventilation system;
• modifying the layout of the work place, for example, by designating areas that are off-limits for diesel engine operation and/or personnel travel; and
• leaving garage doors and windows open (weather permitting)

and, if necessary, the use of respiratory protection devices, will help employers reduce the generation of diesel exhaust into the working atmosphere and the number of employees exposed.

6. Respiratory protection equipment

Where there is a hazard to an airborne hazardous substance, the Canada Occupational Health and Safety Regulations^{Footnote 9} require that the employer provide a respiratory protective device that is listed in the National Institute for Occupational Safety and Health Certified Equipment List and a respiratory protective device be selected, fitted, cared for, used and maintained in accordance with the Canadian Standard Association Z94.4 Selection, care and use of respirators Standard requirements. However, the respiratory protective device should only be used as a last resort.

7. Monitoring and verification of the effectiveness of the control methods^{Footnote 10}

Since there is no scientific consensus on what components of diesel exhaust should be measured to accurately assess employee exposure and there is no established Threshold Limit Value or occupational exposure limit for diesel engine exhaust emissions, it is essential that control measures used to eliminate or reduce exposure of employees to the carcinogen be effective to the fullest extent possible.

Although the quantity and composition of diesel engine exhaust emissions vary depending on the type of engine, the composition of the fuel and many other factors, there are certain indicators that can be used to effectively evaluate the engineering and other control methods used to ensure full protection of employees.

As indicated in the Introduction, there are three types of visible smoke that may be produced during the diesel fuel combustion process: white smoke (water droplets and unburnt fuel), blue smoke (oil and unburnt fuel), and black smoke (soot, oil and unburnt fuel). In addition, the soot content varies depending on the fuel used and condition of engine.

In order to carry out a hazard investigation and assess the effectiveness of the control methods used, or develop a hazard prevention program in the work place, a qualified person should answer the following questions:

1. Are or may employees in the work place be endangered by exposure to diesel engine exhaust emissions?
2. How many employees are potentially exposed to the diesel engine exhaust emissions?
3. What are the sources of exposure and who is affected?
4. What is duration of possible exposure?
5. Have there been any complaints? If so, what are the health symptoms, if any?
6. Have there been any personal and/or area samples taken? Which airborne chemical agents, for example, nitrogen oxides, elemental carbon, sulfur dioxide, have been sampled? What are the concentration levels? Do they exceed the established Threshold Limit Values and/or occupational exposure limits?^{Footnote 10}
7. What is the concentration level of carbon dioxide in the work place? Does the level exceed 1000 parts per million 8-hour time-weighted average?
8. What has the employer done for the control of the diesel emissions to protect the employees from exposure?
9. Is a medical surveillance program for the benefit of employees established in the work place? What does the program include, for example, pre-employment /periodic examination, clinical tests, action levels, health education?
10. Is the employee education program developed and implemented in the work place?
11. How many diesel-fueled equipment/vehicles are operating within a given area? Does or may total engine horsepower exceed the capacity of the ventilation system in place?
12. Are the engines running at full speed and/or left idling? Why? Can the speed be limited and/or unnecessary idling restricted?
13. Are there designated areas for diesel engine operation and/or personnel travel? Are the work place layout modifications feasible?
14. When possible, are the garage doors and windows kept open?
15. Is any visible white, blue or black smoke in the work place? Are the engines serviced and tuned on a regular basis? If black smoke is visible, have the engines been checked for mechanical problems?
16. Are any visible soot deposits in the work place? Where and how significant? What type of the fuel is being used? What is the condition of the engine?
17. Based on the findings, are the control measures in the work place adequate? If the controls are not adequate, what needs to be done on control strategy to eliminate or reduce exposure?

8. Engineering controls

9. Work practices

In addition to engineering controls, good work practices^{Footnote 11} may help reduce Diesel Engine Exhaust Emissions and hence worker exposures. Examples include:

• always open the garage doors before starting vehicles;
• keep garage doors open (weather permitting) for at least 10 minutes following vehicle operation;
• perform regular engine maintenance on the vehicles to minimize Diesel Engine Exhaust Emissions;
• consider a retrofit program to rebuild diesel engines to generate less diesel particulates when they require major overhauls;
• consider both mechanical performance and emissions data when selecting new engines.

10. Employee education and training

The Canada Occupational Health and Safety Regulations require employers to develop and implement an employee education program with respect to hazard prevention and control at the work place. It is necessary that every employee who is or may be endangered by exposure to Diesel Engine Exhaust Emissions be given instruction and training on the health hazard and on the proper use of control measures.