Students’ Corner – Effect of Smoke on Human Behavior

Posted: July 16, 2015 in Fire Protection, Fire Science
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by: Michael Harris

There are many methods that fire protection engineers can use to calculate egress time. One popular method taught is hand calculations that are based off of fluid dynamics (these can be done on a computer also). Unfortunately, this method does not take into account human behavior. There are many factors in a fire that can affect human behavior and egress time. One big factor is the toxic smoke produced by a fire.

Tadahisa Jin and Tokiyoshi Yamada (Jin and Yamada, conducted an experiment in Tokyo, Japan on the effects of human behavior in smoked filled corridors. This study attempted to produce as accurate results as possible by using 31 human subjects, aged 20 to 51, as oppose to animal subjects that previous smoke inhalation studies had used. The experiment was done in a straight corridor that was 11 m long, 2.5 m wide, and 1.2 m high. Certain stopping points were arranged in the corridor where the occupants were meant to stop and answer a simple arithmetic question. While in the corridor, the subjects were exposed to different levels of smoke and radiated heat. The inside of the corridor was also illuminated with fluorescent lamps.

To protect the subjects, a 16 layered towel was positioned on their nose and mouth. This provided a filtration of approximately 90% of the smoke from the environment. Additionally, the subjects had no prior knowledge of the corridor before, but were told it was a straight corridor with an end and that they could turn around at any point.

The study resulted in 17 of the subjects reaching the end of the corridor. Fourteen of the subjects had to turn around before reaching the end. An additional finding was that the subjects answered the arithmetic question incorrectly at a higher rate when the smoke density was higher. This correlation was almost linear. Finally, the subjects’ correct answer rate increased as they walked farther into the corridor. The experimenters concluded that this effect was due to the subjects becoming more emotionally stable as they acclimated to the controlled environment.

Jin and Yamada’s study resulted in valuable information that helped to better understand human behavior in a toxic gas environment. Close to half of the occupants decided the emotional toll was too high and decided to reverse direction and retreat out of the smoke filled corridor. It is worth noting that none of the subjects were exposed to a true fire scenario, considering that they only had to walk through a straight corridor and were protected from the toxicity of the smoke. A reasonable inference would be to assume that more of the subjects would have turned around in the corridor if they experienced pain due to breathing in the toxic smoke.

One of the most important findings of the study is that occupants will change their path due to the presence of smoke. This action of changing path can greatly increase egress time, and put the occupants at higher risk of injury or even fatality. Furthermore, the subjects’ cognitive ability decreased with heavier smoke. This decrease was strictly due to the emotional stress of the scenario. In an actual fire, occupants of the structure may lose cognitive ability to the point of not being able to find a safe path out.

The silver lining in this experiment is that the subjects’ cognitive ability was found to increase over time as they acclimated to the environmental conditions. Unfortunately, this observation may be inaccurate due to the limitations of the experiment. The possibility exists in an actual fire that the occupants will be exposed to an increasing dose of toxicants. Furthermore, in many structures, an occupant will not have as direct of an egress path as utilized in the experiment.

It is clear from the Jin and Yamada study that simply using fluid dynamics to calculate the egress time is not enough. Fortunately, many fire protection engineers will add a safety factor to help account for limitations such as human behavior. My hope is that future research will eventually give our community better insight into human behavior in fire, and allow for a more quantitative approach to the design of fire safe egress.

Jin, Tadahisa, and Tokiyoshi Yamada, “Experimental Study of Human Behavior in Smoke Filled Corridors.” Fire Safety Science-Proceedings of The Second International Symposium, pp. 511-519, 1989.

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Comments
  1. welchsuoe says:

    Nice article – I always use the cartoon of occupants trying to do arithmetic from the Jin paper to illustrate this point in lectures at Edinburgh, it’s quite memorable…

    Like

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