LO 6-4 Identify and describe the hazards associated with exhaust emissions and outline control practices

1. Exhaust Emissions Hazards

Exhaust Emissions Hazards

The exhaust from diesel engines, especially older ones, can contain noxious gases and very small particles that may create a health hazard when inhaled Figure 22. When not properly controlled, such as by using exhaust extraction fans while running an engine inside a shop, short-term exposure to high concentrations of diesel exhaust and particulate matter can cause headaches, dizziness, and irritation of the eyes, nose, and throat severe enough to disable workers Figure 23. Without controlling exhaust, operating engines in a shop when they are cold, when regenerating aftertreatment systems, or when there are mechanical conditions causing abnormal combustion, diesel exhaust will be many times more hazardous Figure 24. Prolonged exposure to diesel exhaust and particulate matter can increase the risk of cardiovascular, cardiopulmonary and respiratory disease, and lung cancer. Diesel exhaust will also worsen the symptoms and physical state of individuals with existing medical conditions that make breathing difficult.

FIGURE 06-22: Older engines, without particulate filters, can emit heavy amounts of diesel particulate matter observed as soot.

FIGURE 06-23: A properly operating exhaust extraction system must be used whenever an engine is operated indoors.

FIGURE 06-24: A warning label on the driver’s doorjamb about the hazards of exhaust emissions.

Several highly carcinogenic substances produced in the combustion chamber of diesels can cling to exhaust soot particles, where they are delivered deep into the lung tissues Figure 25. In newer engines, the exhaust catalysts in aftertreatment systems can generate carcinogenic isocyanates (HNCO; a category of extremely toxic substances) under some circumstances. Furthermore, when a selective catalytic reduction (SCR) system is used to treat exhaust emissions, dosing the exhaust with diesel exhaust fluid (DEF) breaks it down into ammonium nitrate. From ammonium nitrate, exhaust catalysts form ammonia (NH₃) gas. If noxious ammonia is not converted to harmless water and nitrogen, its presence in the exhaust adds to the hazard of breathing diesel exhaust emissions Figure 26.

FIGURE 06-25: Particulate matter, with unknown but carcinogenic substances attached to soot particles, can carry the toxic substances deep into the lung tissue.

FIGURE 06-26: This exhaust aftertreatment system sprays diesel exhaust fluid into the exhaust stream. Levels of noxious ammonia are identified by the ammonia or NOx sensor near the exhaust outlet.

1.1. Exhaust Emission Hazards (continued)

When working on diesel engines, whether it is in a shop or an underground mine, controls for exhaust emissions hazards include:

• Using dedicated extraction fans connected directly to the exhaust pipe outlet using a tightly sealed hose. Extraction fan operation must be combined with fresh outside air to resupply the shop with air extracted by the exhaust ventilation system.
• Verifying that the exhaust hose collector fits snuggly to seal the exhaust stack or tailpipe.
• Closing off unused extraction hose collector ends to maximize extraction volume to running engines.
• Inspecting the vehicle chassis to verify that exhaust is not leaking out of other points in the exhaust system or from the hose collector.
• Verifying that there are no exhaust leaks from other exhaust system components when running the engine with an extraction fan.
• Limiting the amount of time and speed an engine operates in a shop. For example, if the engine is operated to build up air pressure to release the park/emergency brakes, consider using a shop air supply to fill air reservoirs instead of the engine’s air compressor.
• Designating hard to ventilate areas of a shop or work space off-limits for diesel engine operation.
• Enforcing diesel engine idling restrictions on vehicles near the work space.
• Confirming that exhaust extraction and ventilation systems are working correctly. Immediately report to a supervisor any deficiency or poor performance of the exhaust extraction or ventilation system.
• In underground mining operations, technicians may require specialized PPE for respiratory protection, such as an air-purifying respirator equipped with a filter that is certified to meet a legislated standard for removing air contaminants.
• Performing work or repairs on a cool engine. Hot metal and fluids will cause burns.
• Avoiding work around hot equipment, such as exhaust pipes and manifolds. If such work is absolutely necessary, cover the hot equipment with some insulating protection to prevent burns.

1.2. Video: Extraction Fan