Evolution of Moisture Barrier Use in PPE

By Jeffrey O. and Grace G. Stull 

Firefighter protective clothing has evolved profoundly over the past three decades. While there have been a number of advances in different material technologies and aspects of protection offered to firefighters, perhaps the single least understood area is liquid protection arising from the use of moisture barriers.

Fire departments are placing increasing attention on liquid protection as an issue related to the service life of gear based on continued barrier protection being called into question. To understand how moisture barriers perform, it is first necessary to learn the history leading to the current situation.

Photo Craig Allyn Rose
Photo Craig Allyn Rose

Many years ago, several styles of firefighting protective clothing used coated materials as the exterior layer to keep firefighters dry from the massive amounts of hose spray used in firefighting operations. This practice prevailed, particularly in cooler climates, because being wet was a hazard during cold temperature responses. Water-laden clothing also created additional burdens on the firefighter.

Steam hazards
As clothing and material designs progressed, firefighters recognized the hazards of steam being generated from hose spray onto fires especially in closed, hot environments. Coated materials used in the construction of clothing were included as interior layers to create steam barriers to limit scalding burns from steam or other hot vapor contact.

In fact, the very first use of internal coated fabric layers were known as "vapor barriers" to protect firefighters from both steam and other potentially hazardous gases that evolve during a fire in addition to water and corrosive liquids. Unfortunately, for all the benefits these materials provided, they also made the clothing heavy and contributed to the physiological stress on the firefighter.

In the mid-1980s, new technology became available that recognized that a barrier material did not have to be a rubber-coated material, but could be breathable and still fulfill most of the capabilities for providing firefighters liquid protection. This development led to the advent of microporous-based "moisture" barriers, which were also quickly becoming popular in the consumer and sports apparel industries at that time.

Tiny pores
The millions of tiny pores in the material would keep out water and many other liquids while still allowing moisture vapor to pass through. It was claimed that this moisture vapor transport enabled the escape of humidity generated inside the encapsulating garment and resulted in less stress on firefighters. The new materials were considerably lighter in weight than the rubber- coated vapor barriers, fitting into the trend for lessening the overall burden on the firefighter in terms of clothing weight.

Shortly thereafter, the fire service began to appreciate one relatively old hazard and a newer one requiring liquid protection. Firefighters were increasingly being exposed to liquid chemicals found at all fires and other emergencies where they wore their turnout gear. These chemicals consisted of gasoline, hydraulic fluid, and other petrochemical products as well as pool chemicals, battery acid and even suppression aids such as AFFF concentrates that could cause skin harm.

Additional focus on exposure to these chemicals led the committee responsible for NFPA 1971-compliant protective clothing to implement tests to demonstrate that barrier materials used in clothing would hold out these liquids. At the same time, the expanding large proportion of firefighter calls for emergency medical services gave rise to concerns about exposure to blood and body fluids contaminated with the HIV Virus and various forms of the Hepatitis Virus.

Worker ruling
The ability for moisture barriers to become bloodborne pathogen barriers was further cemented when the Occupational Safety and Health Administration declared that firefighters were considered healthcare workers when they rendered emergency medical aid. It meant firefighters were subject to meeting the new regulations for bloodborne pathogen protection, which required clothing that prevented the contact of blood and other potentially infectious fluids from reaching the wearer's skin or underclothing. The institution of a viral penetration resistance test in the NFPA 1971 Standard established that compliance.

Further to the same issue of liquid protection, it was recognized that clothing materials alone could not be counted on to keep the firefighter dry and safe from exposure to hazardous liquids. The overall design of the garment equally contributed to this type of performance, resulting in liquid integrity evaluations, or what commonly became known as "shower" testing, being instituted for structural firefighting garments.

The test forced manufacturers to reexamine how well front closures, seams and other parts of the garments not subject to the specialized material tests would also keep liquids from reaching the garment interior. The test was not without controversy as its appearance created the perspective that clothing would be subject to deluge of liquid. In reality, the test created a challenge that enabled any penetrating liquid to be easily detected and thus contributed to better design of garments to prevent inward liquid leakage.

Two classes
During the 1990s, there were still two classes of moisture barriers — breathable and impermeable — with this distinction driving an industry debate on the value of clothing material systems that permitted water vapor transport. In a study undertaken by the IAFF, a firefighter task-based human subject field study conducted in Indianapolis showed significant differences in physiological measurements in clothing systems incorporating the two different classes.

The IAFF Indianapolis Field Study resulted in the acceptance of a total heat loss test, which required a minimum level of breathability. At first, the requirement was set to simply remove impermeable moisture barriers from the fire service market. Later, higher levels of total heat loss were established for composites to drive the use of less stressful clothing material systems in turnout clothing as a balance to heavy composites with very high levels of thermal insulation.

While other changes have taken place affecting the use of barrier materials in structural firefighting protective clothing, the cumulative effect of this evolution for instituting liquid protection has been to create a material layer that is subject to large number of qualifications.

First and foremost, the moisture barrier must act as a liquid barrier (water, chemicals and bloodborne pathogens), but it must also meet the intrinsic flame and heat resistance requirements and contribute to the thermal insulation for firefighter safety in hostile environments. In essence, the moisture barrier must meet all of the criteria applied to other layers and then still function as a breathable liquid barrier.

These performance demands create high expectations for the moisture barrier that carry through the service life of the clothing. In the next installment of this series, we will examine durability issues for moisture barriers and the issue of liquid protection provided by clothing under field conditions.

Read: Part 2

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