Over the past few years considerable research energy has been expended to characterize the risk that fire overhaul presents to firefighters.
Here's a look at the methodology the Montgomery County (Md.) Fire/Rescue Service deployed to address this issue. This methodology is a comprehensive overhaul risk-reduction approach, based on common-sense tools and simple metering technologies.
All structure fire scenes contain a wide range of toxic gases, vapors and particulates, many of which have a strong correlation to increased cancer risks. It is not possible with current technology to quantify what is present in fire smoke for two key reasons.
- What is present in smoke depends on what is burning and how it is burning.
- Metering in the overhaul environment is complicated by high humidity, which can affect some sensor readings.
The situation is further complicated by the fact that even in the absence of smoke, dangerous concentrations of hazardous substances may linger.
Firefighting is known to have a significant physiological impact on firefighters. Some of the major impacts include, increased core temperatures that may lead to changes in blood chemistry, and increased cardiac stress.
Working in turnout gear exacerbates these dangers, especially when ambient temperatures and humidity are high. Despite the inherent risk, the fire department still has a mission to complete, and risk reduction cannot be allowed to degrade mission effectiveness.
The focus of MCFRS's approach is balancing between physiological and chemical hazards. When firefighters are operating in turnout gear or chemical protective clothing the IAFF notes, "high ambient heat and humidity are conditions that present a heat stress hazard to the entire body."
IAFF further recommends, "If protective clothing (fire or hazmat) is worn, an adjustment factor of 10 degrees Fahrenheit should be added to the environmental temperature before the apparent temperature is calculated."
This assumes that fire smoke is a hazardous substances and the only reasonable protection from those hazards is the use of SCBA. Therefore, whenever there is visible smoke, personnel must use their SCBA.
MCFRS uses a heat-index criteria to establish a baseline for determining when the heat stress on firefighters is sufficient to warrant making trade-offs with SCBA use. When the heat index is less than 80 F, the trade off is no longer worth it.
Based on this information, MCFRS allows the downgrade of personal protective equipment when the combination of relative humidity and air temperature (plus 10 F), known as the heat index, is 80 degrees or higher and the other risk reduction methods are in place.
When the heat index conditions are met firefighters are allowed to replace their SCBA with a particulate mask and trade out their turnout coat for a long sleeved shirt.
Mitigating chemical hazards
Understanding that the physiological dangers are only a part of the larger puzzle, the department established some baseline risk control measures and uses a specific multi-sensor meter configuration to rule out the more immediately dangerous gas or vapor hazards.
To meet the second half of the downgrade criteria, MCFRS mandates the use of forced ventilation with electric fans throughout the entire overhaul process. Forced ventilation reduces the concentration of gases, vapors and particulates in compartments, thereby reducing risk. And, it must be in place before any meter readings can begin.
Once ventilation is in place and the metered environment is smoke free, one person is designated to take readings with a multi-sensor meter configured for the overhaul environment. If the meter goes into alarm personnel must immediately don their SCBA.
Ensuring that the compartment where overhaul is conducted is smoke free is important because it is assumed that the smoke contains hazards at concentrations that only SCBA can protect against. However, ventilation is equally important because the absence of smoke is not sufficient evidence for the absence of respiratory hazards.
Atmospheric metering and monitoring covers four broad hazards: oxygen depletion, volatile organic compounds, carbon monoxide and hydrogen cyanide. While these hazards are certainly not an exhaustive list they are present at all fires and they most certainly represent immediate hazards.
MCFRS also uses a photo-ionization detector to measure for volatile organic compounds typically found in fire smoke.
The oxygen sensor, which alarms at 20.8 percent, is used as a rudimentary chemical detector. When the oxygen concentration is below 20.8 percent either something has displaced the oxygen or an ongoing chemical process has consumed it.
Regardless of the cause, SCBA use is indicated.
MCFRS uses the more restrictive exposure level of 25 ppm for CO. CO levels are not used as a marker for the presence of other hazards but rather as marker for effective ventilation.
CO is slightly lighter than air and mixes well with air such that as the air in a volume is displaced it is reasonable to assume that the CO is displaced with it.
Hydrogen cyanide has emerged as a threat to firefighters, certainly in its own right, but especially when it is combined with carbon monoxide in the bloodstream. The hydrogen cyanide alarm limit is set at 4.5 ppm, which is slightly below the NIOSH time-weight average value.
The photo-ionization detector is used for the nonspecific quantification of VOCs. Using this dramatically increases the number of gases that can be detected.
But because of this technology's limits in this application, the alarm level is set very low at 10 ppm. For perspective, it is possible to get PID readings higher than the alarm level on a person who has just applied a large dose of underarm deodorant.
It is impossible to keep the hazards out of the firefighting ensemble. That makes it important to remove them from the body as soon as possible and to ensure that they are not re-deposited later. Effective hygiene is critical.
MCFRS hygiene rules require the use of wipes to remove gross contamination and avoiding refreshments that require the use of bare hands to consume them.
Personnel are also required to travel back to quarters with the windows partially open to allow trapped gases a way to escape. They are required to use particulate protection when cleaning equipment and hand protection when re-packing hoses and cleaning tools.
Furthermore personnel are strongly encouraged to have a change of clothes with them available to swap dirty shirts on the scene, to clean their gear frequently and perhaps most importantly, to shower as soon as possible.
The fireground is full of hazards and those hazards do not diminish during the overhaul phase of operations.
It would be naive to think that implementing a similar process will prevent future cancers. However, by the application of simple tools and processes the levels of exposure can be reduced without having adverse impacts on mission effectiveness.
This approach is not without some known pitfalls. There are many more details to consider.
For example, our metering technology cannot detect acrolein at time-weight average levels. So when there is any tearing, it is assumed that acrolein is the cause and SCBA use is mandated.
Furthermore, research into this subject continues and the organization will make changes to this approach as the evidence reveals the need.