Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 4: Evaluating Exposure Pathways

In Part 4 of this 6-part series, we will be looking at the concept of Exposure Pathways and Routes of Exposure as a prelude to discussion in Part 5 of your department’s options to minimize chemical concerns, especially as they pertain to diesel exhaust, fire-related carcinogens, and the handling of hose and turnout gear. 

After thoroughly cataloguing equipment and identifying potential contaminant sources, as outlined in Part 3 of this series, the next step is to begin documenting the spread of these contaminants within your facility, to determine your mitigation needs and opportunities. Be mindful that transparency in your inspection and hazard identification process will go a long way toward building trust in your department, as you address potential exposure risks though procedural change and/or facility adaptation. Key to this effort is the systematic identification of possible exposure pathways associated with each contaminant source, and routes of exposure by which individuals may be exposed to chemical contaminants.

After identifying the contaminant source, begin to look at how that contaminant goes on to interface with its surrounding environment. From the source, the contaminant can either spread or be contained. It can become increasingly concentrated or can be mitigated as it moves within your facility. For instance, ventilation can be used to mitigate the contaminant, but in the absence of effective ventilation, the contaminant can become more concentrated over time or when there are multiple sources in the same area. These are examples of Exposure Pathways. 

Exposure Pathways example

Let’s consider a typical pumper as an identified source. The diesel-powered apparatus starts up and leaves the station, returning potentially contaminated from a call. It is parked in the bay, the engine is turned off, the firefighters dismount and take any required steps for decontamination of the equipment and/or gear, and prepare for the next call. Once the next call is received, the apparatus is driven out once again, and the cycle repeats. Additionally, in many stations, apparatus equipment checks are done daily within the bay and may include start-up within the station without actually leaving on a call.

So where are the concerns? As discussed in Part 1 of this series, engine exhaust contains diesel particulate matter (DPM), as well as a large number and complexity of gases and semi-volatile compounds, that are released into the apparatus bay whenever the apparatus starts up, leaves or returns to the bay. From the apparatus bay, these contaminants can travel to offices or living areas. They can also move into decontamination, laundry and storage areas, or be entrained into air intakes or exhausted outside.

Diesel exhaust gases will generally move with the air stream, following the path of least resistance to air movement. DPM, which is very fine, will do the same to some extent. However, some of it will also settle out onto surfaces, equipment, and turnout gear. Other sources of airborne contaminants in your facility may include outdoor sources, such as diesel exhaust from a nearby freeway, and molds or mold-related volatile gases from the storage of wet gear and hoses. These will behave in ways that are similar to diesel exhaust from apparatus in the bay, depending on their composition.

Routes of Exposure

The ways that people can be exposed to contaminants are termed Routes of Exposure, which are ultimately an extension of the environmental exposure pathway into the person. For instance, airborne diesel exhaust will be inhaled. In the respiratory system, gases will again flow in and out, but entering the lungs will have access to the blood stream, through which they can be transported to other sensitive organs and systems. The lungs may be affected directly, by either short-term irritants or long-term toxins, or other sensitive systems, such as the liver or kidneys, may be affected. DPM may be removed by the respiratory systems’ defense mechanisms or may be deposited in the lungs where again it may have a direct short- or long-term effect, or it may interact with the blood stream.

As stated in Part 1, lung cancer is a primary health effect of exposure to diesel exhaust, but other health risks include cardiovascular, cardiopulmonary and respiratory disease, as well as headache, dizziness, and irritation of the eye, nose and throat.

In addition to inhalation, ingestion and skin absorption are the other two most important routes of exposure in the workplace, which generally both originate in direct skin contact. DPM that is deposited onto surfaces, equipment and gear may be ingested from contaminated hands or absorbed through the skin following skin contact. A more likely source of skin contact with chemical contaminants is through turnout gear and hoses that have become contaminated during fire response or overhaul and which have not been properly cleaned and/or decontaminated.

Developing exposure solutions 

Once the individual contaminant sources have been identified, along with the potential pathways that each may take around the facility and into contact with personnel working and living there, solutions can be developed. By identifying these exposure pathways, progress can be made towards solving this complex equation. For instance, when an engine is running in the bay, some level of diesel particulate is exhausted into the apparatus room atmosphere. The extent to which this occurs will vary depending on many factors, including whether ventilation—either diesel source capture, dilution or a filtration system—is used. Other factors, such as numbers of apparatus, facility layout, and pressure differentials between bays and living areas, must also be considered.

To add another layer of complexity, in many jurisdictions, apparatus washing must occur indoors to avoid storm water pollution. In this case, potentially contaminated wastewater is falling onto the slab, potentially on the responder’s uniform or boots, and then down the drain—if you are fortunate enough to have appropriate apparatus room drainage!

One way to minimize the complexity of evaluating exposure pathways is to start by diagramming the pathways taken in the distribution and movement of each contaminant source, as part of a site conceptual model. This is described in more detail in Chapter 6 of the Agency of Toxic Substances and Disease Registry (ATSDR) Public Health Assessment Guidance Manual (2005 Update). This document provides a very useful discussion of this concept of evaluating exposure pathways and routes of exposure, in much more detail than can be provided in this article.

How likely are your mitigating measures to be successful? When thinking of control and mitigation strategies, visualize a door in a wall that separates two areas. Is the door wide open, with completely uncontrolled movement of contaminants? Or is the door cracked open, mitigating most of the problem to within an OSHA Permissible Exposure Limit (PEL)? Or are there available approaches specific to your unique circumstances that allow the door to be shut entirely, or with weather stripping?

For example, let’s consider again the apparatus exhaust as a source of airborne diesel exhaust exposure. Even though it may not entirely shut the door, the use of some type of ventilation system will take the door from wide open to partially cracked, with the goal toward limiting airborne exposures to DPM and gases to within the PEL. As another example, the use of appropriate techniques for cleaning and/or decontaminating equipment and gear can effectively crack the door and may even shut it if an easily cleaned hard surface is involved.

In Part 5 of this series, we will examine in more detail your options for control, following up on this thought process of evaluating exposure pathways and trying to close the door to exposure as much as is reasonably possible. We’ll consider the kinds of options currently available for controlling both airborne and contact exposures, their uses, and their relative effectiveness. And we’ll look toward the future, in terms of new and evolving technologies. Then in Part 6, we’ll wrap up by considering your options for verification of control effectiveness, documentation and communication.

Related Articles:

• Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 1
• Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 2: Taking a Systems Approach
• Confronting Fire Department Diesel Exhaust Exposure Concerns—Part 3: Determining Exposure Sources
• Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 4: Evaluating Exposure Pathways
• Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 5: Maximizing Your Resources
• Confronting Fire Department Diesel Exhaust Exposure Concerns - Part 6: Air Testing & Communication of Exposure Results
• Confronting Turnout Gear, Equipment Contamination in the Fire Station