Hair Fire InvestigationsClean, dry human hair will burn with a flame, although slowly. However, both men and women use many different hair products.
Dr. Fox has investigated at least five hair fires, mostly on women but one on a teenage male. Ignition sources vary from candles to lighting cigarettes to electrical appliances. In some instances the hair will catch on fire while the hair is still wet from the carrying solvent of the hair product, such as the alcohol that is commonly used in hairsprays. In those wet instances, the carrying solvent (alcohol) greatly enhances the flammability of hair and most hair products warn to avoid ignition sources until the hair is dry. Unfortunately, that type of warning leaves the impression that ignition sources do not need to be avoided after the hair is completely dry.
Once the carrying solvent of a hairspray evaporates, what is typically left behind is a light coating of an organic polymer dispersed throughout the hair. It is this organic solid residue that holds the hair together, and is in fact the material for which the hairspray was purchased. Hairspray without this solid organic residue would be pretty much useless as a hairspray.
Almost without fail, the organic solid residue of a hairspray is flammable (capable of burning with a flame). The fact that hair fires deal with solid hair and solid residue often leads to underestimating the flammability of the combination. One might think of the combination of hair plus hairspray residue as “combustible” because they are both solids. However no heat is needed to ignite the mixture. This is due to the high surface-to-volume ratio of the hair plus hairspray residue. An analogy is a lump of coal. As a lump, coal needs to be heated in order to burn. However, if the coal is converted to coal dust with a high surface-to-volume ratio, not only does coal not need to be heated in order to ignite, it is often explosive.
One of the most common characteristics of hair fires is that they are unexpected. Rarely does anyone set his or her hair on fire intentionally. Therefore, when a hair fire happens, the person is caught completely off guard and very often their instinctive reactions make it worse. The most immediate preferred reactions would be to immediately douse the head with water or to smother the fire with a towel, blanket or other suitable material. However, what typically happens is that the person will run about or drop and roll, which only fans the fire with air. Another reaction to a hair fire is to attempt to put out the fire by the use of hands, which typically results in hand and arm burns.
Because burning hair will often “drop down,” the person receives burns to the neck, shoulders and chest, sometimes to a greater degree than burns to the scalp. The individual’s clothing may also catch on fire exacerbating these types of neck, shoulder and chest burns.
Another characteristic of a hair fire is that the person often believes they have successfully extinguished the fire and will stop their efforts to put out the fire only to find that it “re-ignites” In reality, the hair fire does not “re-ignite,” but was never completely put out in the first place. If any small portion of the hair remains on fire, it will “re-ignite” the remaining hair.
A final characteristic of hair fires is severe disfigurement requiring extensive plastic surgery to correct.
The following test methods developed by Dr. Fox are focused on hair products that are applied to the hair and then left on the hair for a period of time that could be hours or days. In other words, the more volatile components of the hair product have evaporated leaving behind a solid, semisolid or nonvolatile liquid residue. However, the same methods can also be used to determine the flammability of hair products before they dry.
Methods to test liquids, such as standard flash point test methods, while they might be useful supplemental tests, do not directly apply to situation involving materials with high surface-to-volume ratios. For example, taking a sample of the bulk solid, semisolid or liquid and testing it for flammability might be a useful place to start. However, the materials also need to be tested in the high surface-to-volume ratio that exists when dispersed on hair.
One such method is to coat glass wool with the hair product. Glass wool alone will not support a flame even though it has a high surface-to-volume ratio. The method consists of applying the hair product to the glass wool and then allowing the coated glass wool to dry overnight. The glass wool plus dispersed dried product can then be tested with a flame to see if it will ignite.
The video below illustrates a preliminary test on a typical hairspray. After being applied to the glass wool, the hairspray was allowed to dry overnight. Clearly, the organic polymer residue deposited by the hairspray burned rapidly with a flame and hence was determined to be “flammable.”
A more realistic test is to use human hair instead of glass wool. The main difference is that unlike glass wool, clean dry hair will burn, although slowly. Therefore, it is important to make the human hair test more comparative and quantitative in nature. For example, the flammability of clean dry human hair should be compared to the same human hair with the hair product.
Human hair can be obtained in the form of human hair wigs, cut hair from beauty salons, or hair taken from a specific person. If the hair fire being investigated involves a specific individual, using the hair from that individual would be the recommended approach whenever reasonably possible. Since shampoos and conditioners and other hair products can affect the flammability of hair, it is important that all such parameters be controlled to the degree possible. .
In the specific example discussed here, a large sample of hair was collected from the woman who was directly involved in a hair fire. In other words, it was her hair that caught on fire. She was instructed to let her hair grow and to also use the same shampoo and conditioner (and any other products) that she had always used. On the day that she cut her hair for the investigation she was instructed to do everything the same as on the day of the fire except to not apply any hairspray. This included taking a shower that morning and using the same shampoo and conditioner.
Once received, the hair was prepared into two equal amounts (weighed to 0.01 grams) and these two samples were placed in two separate disposable aluminum pie pans that were instrumented with three thermocouples.
Only one pan of hair was sprayed with hairspray. The weight of the hairspray dispenser was weighed before and after the hair was sprayed in order to quantify the amount of wet hairspray used. The hairspray was a solution of an organic polymer in mostly ethanol. The treated pan of hair was then weighed with time until the weight stopped decreasing.
While the organic polymer is expected to be flammable and add fuel to the hair, the relative percentage of added fuel is on the order of 2-3%, which is not a large percentage.
Care was taken to ignite each pan of hair (treated and untreated) in exactly the same manner and location. The results were recorded using a data logger and video camera.
The temperature data from the three thermocouples were averaged and the plot below presents the time vs. temperature data from the comparative tests. The fire is ignited at the point where the temperature begins to rise.
Temperature versus time of clean hair and treated hair
It is obvious that dry hairspray residue makes hair burn faster and hotter. That conclusion is based on raw, physical, objective data and is not subject to various interpretations.
Dr. Fox is a Certified Fire & Explosion Investigator and chemical expert with extensive experience in OSHA, EPA and DOT chemical regulations and chemical safety. He specializes in complex industrial chemical accidents, fires and explosions as well as chemical-related consumer product injuries.
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