Archive for August, 2015

by: Nathan Pascale

 

When analyzing the effect of toxicants, there are a few trains of thought that we must consider. First, there are the biological effects. How does the human body process the harmful byproducts that are be produced during a fire and how effectively can it do so? This perspective looks exclusively from an organic point of view, only taking into account functions within the body. The second consideration is for behavioral influences. At a micro scale level, this could be linked to the biological effects as far as how the toxicants can debilitate the brain’s capacity to function normally. However, in taking a big picture point of view this can simply be defined as changes in an individual’s decision making and the actions they take as a result of the toxicants. Finally, in the grand scheme of a fire scenario, we can look at how these biological and behavioral variations can affect the overall tenability analysis of a particular building.

As mentioned previously, the main concerns when determining the tenability of the building are the time to impair one’s ability to escape in a timely manner and the time to incapacitation. The time to impair can be correlated to the behavioral consequences of toxicants in a fire. While the panic theory has been largely debunked, a normal individual is still expected to require time to perceive, recognize, respond, and move to a safe area, and this is all without the effect of toxicants. When we introduce that extra layer of complexity, the question of how much time is enough time becomes much harder to answer. There are many factors that vary on an individual basis that can affect the way they react to the problem at hand, one of them being age.

While irritant gases are important to consider in any fire scenario, their effect is very difficult to quantify due to differing opinions in the field and overall lack of data. Thus, for the sake of this argument, I will focus on narcotic gases. Unlike irritant gases, the lethal and incapacitating effects of narcotic gases are much more accessible and quantifiable through research on animal exposure as well as posthumous studies of fatal fires. Narcotic gases act primarily by attacking the nervous system and to a lesser extent the cardiovascular system. The result is a lethargic state, coupled with headache, nausea, or poor physical coordination, followed quickly by incapacitation or death once the body can no longer compensate for the lack of oxygen being supplied to the brain.

Carbon monoxide (CO) is a toxicant present as a byproduct of all fires. Many deaths have occurred due to CO inhalation where the victims are asleep or inactive for a duration of time before becoming aware of the danger. A model developed by Professor David Purser in 2008 showed that active subjects with greater respiratory minute volume (RMV) rates were much more susceptible to the effects of CO than subjects at rest. When an individual is remote from a room of origin that has undergone flashover, toxicants are inhaled while in a sedentary state until the danger is recognized. At this moment, the exposed individual tries to escape, at which point the effects of the increased respirations an environment laden with CO begin to cause severe impairment or incapacitation.

Elderly individuals are also more likely than the average adult or child to have conditions such as asthma or coronary artery disease. A study conducted by the EPA in 2000 determined that the tenability limit of carboxyhemoglobin (the amount of CO in your blood) for an individual with coronary artery disease is only 5%, while the limit for an average adult is 30% (Purser 2008) and 25% for a child (Klees 1985). Additionally, according to an SEFS report, elderly individuals are expected to spend more time in their bedroom then adults and children. The fact that elderly people are more vulnerable due to physical condition, preexisting health concerns, and that they spend more time in the bedroom environment when exposed to fire conditions, we can conclude that elderly individuals comprise the age group at the greatest risk of death and injury when faced with narcotic gases.

In conclusion, there is evidence to prove a correlation between the effects of toxicity and age, but not enough to reliably quantify what those effects are. Preexisting illnesses, physical conditions, familiarity with the building, and susceptibility to toxicants are just a few of the factors that have to be taken into account during a tenability analysis. Unfortunately, due to the harmful nature of toxicants, experimental studies on humans are considered unethical and there is not a large pool of data to analyze for effects on past fire victims. Thus, with the information currently available, the elderly population can be considered most at-risk in a toxicant exposure event, followed by children, and then adults. Consequently, it is my hope that code committees and the fire protection community as a whole takes a closer look at these factors and evaluates the possibility of increasing the required safe egress time, whether it be by decreasing the walking speed, increasing recognition time, or otherwise, for those occupancies and buildings that shelter a large number of elderly people or children.

References

Purser, D.A., “The Effects of Fire Products on Escape Capability in Primates and Human Fire Victims,” International Association for Fire Safety Science, 2008.

Klees, M., Heremans, M., and Dougan, S. “Psychological sequelae to carbon monoxide intoxication in the child,” Sci. Tot. Environ., 1985.

Gann, R.G., J.D. Averill, K.M. Butler, W.W. Jones, G.W. Mulholland, J.L. Neviaser, T.J. Ohlemiller, R.D. Peacock, P.A. Reneke, and J.R. Hall Jr., “International Study of the Sublethal Effects of Fire Smoke on Survivability and Health (SEFS): Phase I Final Report,” National Institute of Standards and Technology, August 2001.