Diesel Exhaust Exposure Concerns - Air Testing and Exposure Results

Throughout the first 5 parts of this series, we have considered the risks of exposure to diesel exhaust, management of personnel exposures, the spread of diesel exhaust through the fire station, and strategies for mitigation.

In Part 6, we will consider air testing, appropriately documented, which is ultimately how we verify employee safety when there is an airborne hazard.

Testing challenges

Although diesel exhaust has an odor and may be irritating to some people at higher exposure levels, your sense of smell is not an accurate method for determining the concentration of diesel exhaust components to which personnel may be exposed. Yes, you may be able to say that there is some diesel exhaust in the area, but you cannot say with any reliability that it is present at either a safe or a hazardous level.

In truth, it is challenging to answer this question even with air testing. One of the reasons for this was discussed in Part 1 of this series. Diesel exhaust is not a simple workplace air contaminant but is a complex composition of dozens of compounds including both gases and particles.

Often people do not realize that there is no test method, Occupational Safety and Health Act (OSHA) Permissible Exposure Limit (PEL), or other reference exposure level for diesel exhaust as a whole. (Unfortunately, we don’t yet have a Star Trek tricorder that will tell us how much diesel exhaust we have and whether it is dangerous to life or health!) We must consider the individual components.

On its Chemical Sampling Information page for Diesel Exhaust, OSHA states that it has no sampling method for diesel exhaust, but instead recommends sampling for several of its components: acrolein, benzene, carbon dioxide, carbon monoxide, formaldehyde, nitrogen dioxide, and sulfur dioxide. For each of these, there is a method of sampling and analysis available from OSHA or the National Institute of Occupational Safety and Health (NIOSH). There is also an OSHA PEL for each of these compounds, so that interpretation of results can be relatively straightforward and meaningful.

In addition, OSHA refers the reader to NIOSH Method 5040, for measuring diesel particulate matter (DPM) as total carbon (with both organic carbon and elemental carbon reported by this method).

It should be noted, however, that there is no OSHA PEL for DPM, nor is there a NIOSH Recommended Exposure Limit (REL). The standard that is referenced by NIOSH is a Threshold Limit Value (TLV) of 20 µg/m³ (as elemental carbon) that was proposed in 2001 by the American Conference of Governmental Industrial Hygienists (ACGIH), but which has since been vacated. The California Department of Public Health Hazard Evaluation System & Information Service (HESIS) also recommends a maximum of 20 µg/m³of elemental carbon [MC3] as a surrogate for diesel exhaust exposure. While there may not be complete agreement on the use of this reference standard, it is widely used.

NIOSH has also published NIOSH Method 2560, which measures 1-nitropyrene as an indicator compound in diesel particulate. However, there is currently no PEL, REL or TLV for 1-nitropyrene. For this reason and others, interpretation of results by this method is difficult and may be misleading.

Ongoing studies

Since the early 90s, NIOSH has been studying the levels of diesel exhaust in fire stations. The following are several recent Health Hazard Evaluations (HHEs) conducted by NIOSH for diesel exhaust in fire stations:

These site-based studies, published by NIOSH industrial hygienists between June 1998 and February 2017, had several purposes: to quantify employee exposures to diesel exhaust components, to evaluate new control technologies by assessing pre- and post-exposures, and to compare indoor and outdoor exposure levels.

The NIOSH researchers used several sampling and analytical methods for the characterization of firefighters’ exposures to diesel exhaust. These included DPM as elemental carbon and 1-nitropyrene, as surrogates for diesel exhaust as a whole. Also sampled were carbon monoxide, sulfur dioxide, nitric oxide, nitrogen dioxide, and volatile organic compounds (VOCs). Particle concentrations by size were measured, and carbon dioxide was measured to assess the effectiveness of ventilation, along with the use of ventilation smoke tubes to visualize air movement patterns.

Of these, the studies listed never identified 1-nitropyrene or sulfur dioxide above the limits of detection, and no overexposures were measured to any of the remaining compounds (carbon monoxide, oxides of nitrogen, and specific VOCs including benzene), except for DPM as elemental carbon.

Other agencies and/or researchers (public and private) have considered this issue of how best to sample for diesel exhaust as a workplace hazard in order to characterize employee exposures. Most have used methods similar to those employed by NIOSH in the HHEs just discussed.

Some researchers have sampled for additional diesel exhaust components. For instance, Bott et al (Queensland Fire and Rescue Service Research Report 2010-01) tested for aldehydes and poly aromatic hydrocarbons (PAHs). PAHs are not considered particularly volatile but may adhere to DPM, and so can become airborne. Also, the generation of diesel exhaust is not by volatilization but by smoke generation, which results in non- or less-volatile components of diesel exhaust becoming airborne, including DPM. Both aldehydes and PAHs were detected at levels below the applicable PELs.

Ultimately, the best current recommendation for evaluating diesel exhaust in fire stations is to sample for DPM as elemental carbon, using NIOSH Method 5040 and the 20 µg/m3 reference level that was proposed by the ACGIH in 2001 and is currently recommended by California HESIS.

Other factors

When conducting air testing, additional issues should be considered, including the length of the shift, station call volumes, types of apparatus being deployed, etc. Depending on the exposure levels measured in living spaces, it may be more relevant to evaluate firefighters’ exposures over a longer shift length than the typical 8-hour shift used by OSHA (or even 10- or 12-hour). In such a case, other sampling methodologies may need to be considered, for comparison with environmental reference standards or with outdoor background levels.

Although background diesel exhaust levels and outside environmental air conditions may not be monitored where your station is located, background monitoring is done in many areas. For instance, in the Puget Sound area of Western Washington, the Puget Sound Clean Air Agency (PSCAA) measures and reports background levels of diesel particulate in the community. As can be seen on their Air Toxics page, DPM represents a considerable portion of the background air toxics in the area. It is important not to forget that, depending on where your station is located, background levels of DPM may be significant.

When sampling to assess personal exposures, you must also consider whether to collect a personal breathing zone sample (generally preferable) or an area sample or “grab” sample. These latter types of samples can be useful if you are concerned about the effectiveness, for instance, of a localized ventilation control or want to evaluate peak or short-term exposures.

You should consider also the use of direct-reading instrumentation versus the standard analytical methods presented here. Direct-reading instruments typically provide quicker results and may be more flexible in terms of sampling time. They can give you both full-shift data and peaks. In either case, to sample properly, you must possess a certain level of familiarity with use of the method and/or instrumentation. If you still have too many questions to do these assessments yourself, assistance may be available through the analytical lab with whom you are working or your instrumentation manufacturer, as well as through regulatory consultants and private industrial hygiene consultants.

Documentation

Finally, documentation is critical. The authors of the studies that have been discussed in this article present carefully documented sampling and analytical methodologies, including methods used and sample locations and volumes. Although they did not include the Laboratory Chain of Custody (COC) form in their reports, this would have been a part of their record, along with sample times and equipment calibration data.

The study authors also stated the purpose of their sampling, described the design and set-up of each station, and identified the date, controls in use and time of day. They described the activities being performed during sampling and equipment movements. They included the reference standards they were using, their interpretation of the results compared to those standards, and their conclusions and recommendations for the future. When you are doing your own sampling, it is necessary that you document and maintain each of these pieces of information.

In closing

This 6-part series of articles has covered the evaluation and control of diesel exhaust risks and exposures. Next month we will present a bonus article, which will address one final important topic. This is the handling and storage of contaminated gear (turnout gear and personal protective equipment, fire equipment, and tools). It will also consider ways to effectively communicate your overall assessment results.

Related: