Whether it's driving behind an 18-wheeler or standing next to an idling school bus, we know it the instant we smell it - the acrid, nauseating odor of diesel fume. Our bodies seem to know instinctively that it's unhealthy and most likely should not be inhaled. However, it remains the case that most people are not aware of what diesel emissions consist of, let alone the various health problems associated with exposure.
Constituents of diesel exhaust
Diesel exhaust (DE) is a complex mixture of particles, vapors, and gases. In fact, it is a mixture of hundreds of compounds existing in either gas or particle form.
Gases can include the following:
- carbon monoxide
- nitrogen compounds
- sulfur compounds
- polycyclic aromatic hydrocarbons (PAHs)
As for the particles, they are made up of a center core of elemental carbon and materials adsorbed onto its surface, including organic compounds as well as sulfate, nitrate, and metals.
Deisel particulate matter (DPM) is made up of fine particles (<2.5 microns in diameter) as well as ultrafine particles (<0.1 microns in diameter). These particles have a large surface area, which makes it very easy for various compounds to become adsorbed to the surface.
The small size of these particles means that they are highly respirable and can travel deep into the lung.
The contents of diesel emissions can vary significantly depending on the type of combustion engine used, the variety of fuel, and the activity of the machine.
The acute short-term effects of diesel exposure include acute irritation of the eyes, nose, and bronchial passages. Neurophysiological symptoms include lightheadedness and nausea, and respiratory symptoms include cough and phlegm production.
Data from animal studies has led many to conclude that diesel emissions are carcinogenic to humans. The small particle sizes have been shown to increase the rate of asthma in populations where diesel emissions are prevalent (urban centers).
The EPA has provided an estimate as to how much a person can be exposed to diesel particulate matter (DPM) without being likely to experience noncancer respiratory effects. This is known as the "reference concentration" (RfC), and is currently estimated at 5 micrograms per cubic meter of air.
As of the writing of this article, there are no legal exposure limits for deisel emissions. In 2001, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended an upper limit of 20 microns per cubic meter of air. This was later rescinded following lawsuits and pressure brought from industry leaders.
The following table presents existing upper limits for various individual diesel constituents:
|Substance||CAS#||OSHA PEL||OSHA 88*||MSHA TLV||ACGIH TLV|
* - not legal limits (PELs adopted in 1988 were later remanded by court)
a - for metal/nonmetal mines
b - for coal mines
d - 15-minute short term exposure limit (STEL)
(C) - Ceiling value
A2 - Suspected human carcinogen
The absence of a single, somewhat simple concentration of DPM makes it rather difficult to measure exposure risks. The problem with this separation of individual deisel emission components is that it is highly likely that the whole mixture acts in a synergistic manner rather than simply a collection of various isolated pollutants. In other words, the collection of contaminants most likely has greater hazard potential than simply the sum of its individual pollutant parts.
The encouraging news is that experienced Certified Industrial Hygienists are adept at looking at these disparate contaminants and assessing whether or not an exposure hazard exists. Even without a clear-cut legal exposure limit, it is possible to make some sort of judgment as to whether the diesel exposure is high, even though individual pollutant levels are at "acceptable" concentrations. An industrial hygiene assessment should be performed if diesel equipment is operating in an area that is not well ventilated or if several diesel engines or operating in close proximity of one another. If you have a questions about diesel exhaust exposures at your facility please contact us using the request button below. One of our professional staff members will resond within 1- 2 business days!