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

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.