Questions often arise as to how easy clothing becomes contaminated on the fireground and if there are differences in the level of contamination for the same items of a protective ensemble. The issue frequently comes up in distinguishing between rubber and leather footwear, but it is a reasonable inquiry for the overall clothing system.
We have looked at contamination of different materials and can offer some insight to help firefighters determine if they need to be concerned about different exposure events.
Contamination occurs when some unintended substance gets on or in clothing or equipment. It may be minor such as light soiling or intrinsically dangerous like a splash of a strong acid. Contamination implies substances that are unwanted because of their potential health effects.
It is also important to recognize that contamination may be transient, either leaving the clothing on its own with time or through cleaning. The greatest concern is for contamination that is persistent and continues to expose the firefighter to the hazard.
The process of contamination itself varies greatly as does the environments in which the contamination occurs. During a structural fire, much of the contamination is in the form of smoke particulate and fire gases.
This form of contamination envelopes the firefighter, contaming all exterior surfaces of the clothing ensemble. The contamination also penetrates various portions of the ensemble, most notably through joints and gaps between different clothing items or closures such as on the front of the coat or pants fly.
Gases and fine particles easily get into interior spaces, so even underlying clothing can become contaminated. The penetration of contamination in this fashion will be more localized where there are easier pathways for entry.
Ensemble areas such as the hood, pant legs and coat-to-pant overlap are common penetration pathways. Places where there are continuous films of flexible material retard this penetration, but some substances can still get through.
Particle sizes
In addition to penetration, there is permeation. This is when contamination moves across a material on a molecular level as opposed to the bulk passage that occurs during penetration. Permeation is more insidious because it goes on unseen, and can occur at relatively high rates causing contamination to spread throughout the clothing.
Large bulk substances such as smoke particles tend to coat surfaces in the form of soot. These products of combustion are particularly hazardous because the individual particles adsorb and retain the chemical gases created by the fire, causing a longer-lasting form of contamination.
The particle sizes in smoke can be a hundredth of a micron, making the particles invisible except in the concentrated aggregate of the smoke cloud. Thus the particles easily penetrate textile materials, but any material with a semi-solid surface, such as rubber or plastic, will generally stop this penetration. On the other hand, leather, which is porous, will allow some penetration.
Gases are more ubiquitous. Given their form at a molecular level, these substances will penetrate textile and leather materials but not plastics and solid films.
Nevertheless, depending on the type of the gas, primarily the size of the chemical molecule and the nature of the material, chemical gases will permeate most materials. Very dense and thick materials will reduce permeation and some materials such as metals will completely resist any chemical permeation.
Firefighters are also exposed to various types liquids of whether through hose spray that has picked up contaminants or broken containers of liquids. Liquids can also penetrate clothing and well as permeate into materials.
Liquid barriers
The ease of liquid contamination depends greatly on the amount of liquid, the characteristics of the liquid, the force behind that liquid and the characteristics of material. Materials may be able stop a small volumes of liquid, but when in large quantities, many porous materials are likely to become wetted and permit penetration.
Some liquids have greater contamination potential because they move more easily over material surface or degrade material due to corrosiveness or their solubility in the material.
Many textile materials used in firefighter protective clothing are treated with repellent finishes that help. However, some liquids with low surface tensions enable the liquid to easily spread on surfaces (instead of beading like water). This allows the liquid to penetrate small openings.
Unfortunately, already soiled and contaminated surfaces allow easier penetration. If there is pressure behind the liquid such as from kneeling in a puddle or the force of hose spray bouncing off a surface and back onto the individual, that pressure will push the liquid farther into clothing, particularly porous textiles and leather.
As with gases, liquids can also permeate by dissolving in the material, even plastic and rubber materials. In some cases, some of these more solid materials can actually retain the chemical longer than can the porous materials.
A firefighter helmet best represents the full range of materials and illustrates how contamination can occur. The hard surface of the shell can be coated with solid soot. This soot coating will adsorb and hold fireground gases.
The same soot will deposit on all exterior surfaces include the faceshield or goggles, reflective trim, ear flaps and exposed portions of the suspension that include a range of plastic, textile and leather materials.
While fire gases will not penetrate or even permeate a hard thermoplastic shell, the gases will enter the helmet through any opening between the shell and suspension, be absorbed by the textile or leather materials and permeate plastics. Similarly, liquids that contact the helmet will be absorbed by any exposed textile or leather components.
Contaminant persistency
The retention of contaminants in clothing and other protective equipment depends mainly on the type of substance and how the contamination took place. Many fire gases are volatile and, while absorbed by soot or directly into materials, will off gas over time, usually at very low levels.
Thus removing the soot not only gets rid of the solid contaminant, but also takes away some of the trapped gases.
Chemicals that are less volatile are more likely to remain in place, particularly if directly absorbed into materials. The increased affinity of the substance for the material can mean that some contaminants can stay for very long periods unless the item is thoroughly cleaned.
One important factor other than substance volatility is the degree to which the contamination is water-soluble. Not all combustion products dissolve in water and therefore rinsing may not be effective. Using detergents and soaps improves non-water soluble contaminants’ solubility in water, particularly for oil-based chemicals.
Yet the ability of a soapy water to penetration and completely wet the material for removing the contaminant is key for addressing persistent contaminants. In some cases other types of cleaning products have to be used to address contaminant issues.
Cleaning expertise
Many clothing items contain a variety of materials. When exposed to the wide range of contaminants on the fireground, including biological liquids not addressed here, these materials will be contaminated to different extents depending on the how much exposure occurs, the manner in which the exposure occurs, the types of contaminants involved and the nature of the materials.
Thus, it is possible that while some parts of the clothing might be cleaned easily, other parts may not. The less cleanable parts of the clothing can then become repositories where contaminants build up.
Cleaning turnout gear properly takes expertise in removing contaminants. Many independent service providers have gained this experience and have found various solutions for removing both general and specific contaminants.
Other resources include the gear manufacturers that can offer specific recommendations in most cases.
But an important consideration is determining their ability to decontaminate effectively, which may rest in addressing all materials in the gear, not just the principal fabric in the case of clothing or the shell of a helmet.
Full removal of contamination means applying a process that addresses the complete item, including all of its materials and understanding the contamination process.
