It’s unlikely that there are any serving firefighters who remember responding to incidents in the traditional wool jackets and PVC leggings that were still in use up until the early nineties. That’s because the watershed moment for development of technology in protective clothing occurred after the tragedy of the Kings Cross fire in 1988. The injuries sustained by firefighters highlighted the need to find more effective clothing solutions.
Since then, the revolution in protective clothing has been unrelenting, driven by continued technical innovation. Today’s firefighters wear clothing made from lightweight fire-resistant fabrics that incorporate systems to manage heat and moisture build-up and mitigate risks such as heat stress, particulate and pathogen penetration that were barely understood all those years ago.
We have seen incredible innovation from outer-shell fabric manufacturers such as PBI, Hainsworth and Dupont, resulting in lightweight heat and flame protection that delivers incredible levels of performance.
However, one of the most significant technical advances in firefighter PPE was the inclusion of a moisture barrier, first developed by Gore in the late eighties. You can’t see it or touch it, but the moisture barrier plays a critical role in managing heat and moisture inside a firefighting ensemble, tackling the risks of heat stress and steam burn. Some moisture barriers, such as the GORE-TEX CROSSTECH range, bring added protection from blood pathogen and particulate penetration.
The moisture barrier was originally incorporated into protective clothing because of its ability to combine waterproofness with breathability. This stops water penetration from outside while allowing water vapour (sweat) to pass through the layers of the garment to the outside.
The pores in a GORE-TEX Moisture Barrier are 20,000 times smaller than a droplet of water but 700 times larger than a molecule of water from perspiration. When the body gets hot it sweats to cool itself. It is the process of the liquid evaporating from your skin that cools the body. For this to work, clothing needs to allow the vapour, which is created by the liquid sweat evaporating, to pass outside the garment. This is what we describe as breathability, as opposed to air-permeability which just lets air pass through a fabric or garment. It plays an important role in mitigating the risk of heat stress by cooling the firefighter.
Activity, or a rapid temperature rise, will trigger the body’s sweating to lose heat. This increases blood flow from the body core to the skin. The body is sensitive to even the smallest rises in body temperature. US military research has shown that once core body temperature of 100°F (37.8°C) is reached, each increase of only 0.1°F is physiologically significant, leading to increased risk of heat exhaustion. As temperature rises, the symptoms intensify from not hearing and reacting to decreasing mental accuracy and speed, all of which put the firefighter at increased risk of harm.
Structural firefighting garments are designed to protect against the most extreme situations, such as a flashover. Garments are regularly tested to withstand direct flame at 1,000 degrees for eight seconds. These tests are always undertaken with dry garments and do not take account of the impact that moisture can have if it is allowed to build up inside a garment.
It’s vital that protective clothing passes the simulated flashover test, but in normal fireground conditions it is possible that a firefighter will be exposed to radiant heat for relatively long periods of time. This heat, or energy, transfers through complex thermal energy mechanisms inside the layers of their clothing. When clothing is then compressed against the skin, for example when a firefighter crouches, kneels or flexes and arm, that energy transfers through to the skin and can result in a burn.
The presence of moisture within structural gear, accumulated from water spray or sweat, is associated with ‘steam burns’ caused by low energy heat transfer. While moisture in the outer layers of a garment takes heat away from the ensemble in intense heat exposure, if the garment is wet or damp inside then the risk of burn injury increases. Water conducts heat 23 times faster than air so any dampness inside the suit will transfer heat to skin very much quicker.
There are many instances of firefighters who have experienced steam or compression burns as a result of stored thermal energy inside a garment. In most cases, there is little or no damage to their garment. It is the breathability in the garment, which comes via the moisture barrier, that provides the necessary cooling and vapour transfer to mitigate these risks.
Moisture barrier technology plays a vital role in mitigating a range of other risks beyond moisture that were not fully understood 30 years ago.
When the UK government set up Firebuy in 2005 to deliver the national Integrated Clothing Project, the risk profile for firefighting identified exposure to blood pathogens as the top risk, above heat and flame. This reflected the increasing proportion of responses to rescue incidents, rather than fires where exposure to blood and chemicals is much more prevalent.
Gore introduced CROSSTECH Product Technology into its moisture barriers to protect firefighters from blood-borne pathogens and common chemicals. They achieve a 100% pass rate on ISO 16604 method C test for blood-borne pathogen protection.
In recent years, there has been a focus on the danger of particulate contamination in fire gear, which is another risk that the moisture barrier protects against. Smoke particles are the by-product of fire decomposition, and depending on the nature of the fire, materials and environment, can contain a range of different high-risk substances. These include hydrocarbons such as methane or benzene, dioxins and furans, hydrogen cyanide, sulphur oxide, recomposed particles (PAHs) as well as carbon monoxide and carbon dioxide. The content and distributions of contaminants varies from fire to fire and will change by the minute at every fire.
GORE-TEX Moisture Barriers with CROSSTECH Product Technology offer particulate blocking performance against fireground particulates. The NFPA 1971 2018 Edition standard recognises the importance for testing particle penetration. It has introduced a system level test to evaluate an ensemble design as well as a particulate-blocking test used to evaluate particulate-blocking layers in an optional particulate blocking hood. The modified ASTM2299 testing, which was introduced to test firefighter hoods, uses a particle size from 0.1μm to 1.0μm to assess the efficiency of the particle blocking layer. It requires a minimum 90% performance to pass the test. When tested, the GORE-TEX Moisture Barrier with GORE CROSSTECH Product Technology achieved 99.9% blocking efficiency when evaluated using the particulate blocking test.
Since it was first introduced to garments all those years ago, moisture barrier technology has continued to develop to meet the protective needs of firefighters as the risk profile evolve. The technology is critical to firefighter safety and wellbeing.
For more information, go to www.goretexprfessional.com
About the Author
Suzanne Prince is the UK Fire Associate for W.L & Gore & Associates.
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