By Jeffrey O. Stull
FireRescue1 Columnist
Sponsored by Globe
 Photo Mike Meadows |
Structural firefighters have a number of footwear choices available. In general, there are a variety of different features for footwear uppers, soles, barriers, and lining packages. But much of this footwear is usually classified as rubber versus leather.
While both types of footwear are required to meet the requirements of NFPA 1971, Standard on Protective Ensemble for Structural and Proximity Fire Fighting, the two different types of footwear achieve compliance in different ways, attributable to their materials and designs.
For example, rubber footwear by virtue of its overall construction provides integrity against liquid leakage by the exterior rubber coating on its outer surfaces. In contrast, leather boots must use a barrier layer underneath the leather to provide continuous liquid protection to the foot.
The construction methods used in both types of footwear vary dramatically. While both footwear types are constructed using a last, a mold or form in the shape of a foot, footwear manufacture differs in how materials are joined together and the overall steps in preparing finished footwear.
Firefighter preferences take into account a variety of factors that include overall weight, comfort and fit, styling appeal, protective performance, durability, and cost. As with the selection of any firefighter footwear, the determination of the most important characteristics involves a series of tradeoffs.
The weight of footwear has become a topic to some as the fire service seeks to find ways of reducing the stress imposed on firefighters. Stress reduction has already been identified as a principal goal in firefighter PPE selection as consideration is given to products being breathable and lighter.
For footwear, the argument is that items of PPE that are worn farthest from the firefighter’s center of gravity impose the greatest potential stress to the firefighter in terms of weight and burden. Some research has indicated that a reduction in 1 pound of footwear is equivalent to reducing 5 pounds of weight from the firefighter’s back.
IAFF study
In general, rugged tall boots are heavier than boots that are form fitting and made of lighter materials. In a 1980s study commissioned by the IAFF, the University of Delaware found higher energy expenditure by firefighter test subjects wearing then available rubber footwear compared to leather footwear. Nevertheless, not all field studies have shown relatively little differences in subjective ratings between leather and rubber footwear.
Furthermore, both rubber and leather footwear providers have endeavored to find ways of lightening the relative weight of their products. For example, certain rubber formulations and the design features on rubber footwear help reduce weight. In the case of leather footwear, the use of non-leather upper textile materials with lighter weight reinforcement has made some footwear products lighter. Both types of footwear benefit from improved composite hardware inside toes and outsoles.
Fit and comfort are probably some of the more closely perceived factors associated with the choice of footwear. A firefighter who has uncomfortable footwear is not likely to be an effective firefighter.
While the NFPA 1971 standard remains progressive in requiring that footwear manufacturers provide footwear products in a full range of sizes for both men and women, including half sizes and three widths, footwear fit is a matter of personal preference and experience.
For some firefighters, rubber footwear which may tend to be less form fitting compared to leather footwear is considered perfectly adequate in terms of its ankle support and comfort. Yet other firefighters might require closely conforming footwear to prevent blisters and wearing discomfort.
The relative flexibility of leather combined with lace-up designs and other footwear features enable leather footwear to often better conform to the firefighter’s feet, but some rubber footwear manufacturers have developed innovative designs to close this gap.
The key aspects of footwear performance include insulation from heat (and cold), maintenance of liquid integrity, and physical durability. The levels of insulation provided by footwear that keep the feet warm in the winter or cool on the fireground has less to do with the general type (rubber versus leather) than it does the actual construction for that specific style of footwear.
In both types of footwear, the primary insulation is provided by linings. The thickness and placement of these linings will affect insulative qualities, though both styles of footwear generally perform extremely well as compared to other PPE items.
Potential problems
Problems can occur when extremely thin insulation packages are chosen or the insulation is non uniform over the entire boot. Rubber boots tend to provide more consistent liquid integrity only because the liquid integrity usually coincides with the height of the footwear. In contrast, leather footwear that uses a barrier on the boot interior may not extend to the full height of the boot depending on the extension of the barrier layer and the closure features used in the design of footwear.
For example, where a gusset is used to aid in footwear donning, the lowest points of the gusset may be the where the overall height of liquid protection stops. It is further important that pull tabs and other donning aids not be sewn through the barrier layer creating pathways for liquid leakage.
Rubber boots tend to be more durable than leather ones, being able to withstand abrasion, cuts, and puncture more readily, but leather boots that are properly maintained also provide long service life.
One area of concern for all footwear involves the issue of chemical contamination and cleaning. Both rubber and leather are affected by chemicals adversely. It is difficult to provide a very specific answer if one material is better than another because the ability to decontaminate boots depends on many factors including the chemical(s) involved the exposure, the manner of exposure, the condition of the footwear, and how the footwear is maintained.
Leather is a porous material and as such it will “absorb” many chemicals. The ability of leather to absorb chemicals will be affected by the surface tension of the chemical. Lower surface tension chemicals (such as many hydrocarbons) will tend to penetrate the leather more easily than water-based ones.
The leather’s resistance to penetration by chemicals will lessen as the original finishes and polish wears off. Depending on the volatility of the chemical and the care of the boots, the chemicals can remain in the boot leather.
Highly volatile chemicals, such as hydrocarbon solvents (e.g., hexane, benzene, and gasoline) will tend to evaporate from the boot leather. In contrast, less volatile chemicals such as creosol and naphthalene may tend to remain in the leather until high temperature exposures drive these chemicals out of the leather.
While there is a moisture barrier to the inside of the leather, the moisture barrier does not prevent permeation — the passage of chemical molecules through a material — of the chemicals. However, the amount of permeation will be low unless the chemical exposure is sustained over a long period of time and the exposure concentrations are high. Nevertheless, the moisture barrier does prevent the penetration of liquid chemicals and ensures that even very small amounts of liquid do not contact the foot.
Chemical absorption
Rubber is equally affected by chemicals. In this case, chemicals “absorb” onto the surface and permeate through the material. The Neoprene rubber that is used as the principal rubber in firefighter boots is particularly susceptible to certain chemical classes.
For example, organic acids (formic and acetic acid), aldehydes (formaldehyde), amides (dimethylacetamide), amines (ethyl amine), esters (acetone), halogenated hydrocarbons (chloroform, carbon tetrachloride), aliphatic and aromatic hydrocarbons (hexane, benzene, gasoline), and nitrocompounds (nitropropane) readily permeate Neoprene materials.
Neoprene generally resists permeation when exposed to ethers (ethyl ether), inorganic salts (sodium hypochlorite), inorganic bases (sodium hydroxide), and inorganic acids (sulfuric acid). When exposed to chemicals, the rubber can swell and deteriorate, which in turn increases the rate of permeation. Also, if a rubber is not cleaned (as with leather), the chemical stays in contact and will continue to permeate and degrade the material.
The general procedure for decontaminating boots is to rinse with water, wash with a liquid detergent such as Tide and scrub the surface with a soft bristle brush. The boots should then be air-dried for at least 24 hours, preferably at an elevated ambient temperature (100 – 120 F) to drive off any volatile chemicals.
Decontamination effectiveness is significantly affected by the chemical’s volatility and water solubility. Chemicals that are volatile will evaporate. But chemicals that don’t evaporate, such as oily chemicals, will tend to stay in the leather and contaminate the rubber matrix.
The general decontamination procedures won’t be that effective for chemicals that have permeated the material matrix that are also water-insoluble and of low volatility. Even given apparent decontamination of the PPE, there are no standards for how much chemical must be removed and what residual levels of chemical remaining in the boots is considered acceptable.
The important aspect of choosing between rubber and leather footwear is weigh your organization’s needs and decide which characteristics are more important – weight, comfort/fit, performance, durability, contamination resistance, and cost.
Some of these characteristics can be determined by understanding other departments’ experiences with specific styles of footwear and the relative service provided by the footwear. As with any type of personal protective equipment, it is difficult to achieve 100 percent satisfaction between all firefighters. However, it is important that all firefighters be afforded proper fitting footwear that provides an acceptable level of protection without compromising their safety.
