Does More Strength Equal Durability?
The same inverse relations can be said for fabric strength and its impact to comfort by limiting the THL performance of 3-layer composite systems (outer shell, moisture barrier & thermal liner). Over the past few years, the industry is seeing stronger outer shells with tensile and tear strength numbers that are 3-4x the requirements in the NFPA 1971 standard.
Do these higher strength numbers provide more durability and if so, what is the trade-off for the increased strength?
The National Fire Protection Association (NFPA) recognizes the importance of fabric strength (tensile and tear strength) and sets minimum requirements for performance. These requirements make outer shells in PPE the strongest materials in any industry.
Based on our years of manufacturing experience, we, at Fire-Dex, believe that at some point, a fabric is strong enough to withstand the demands of the fire service. Exceeding that point can compromise other more important attributes – mainly comfort and THL.
The ultimate goal for TECGEN71 was to create the most flexible, lightest weight, highest THL composite systems in the market without sacrificing thermal protection or durability in the process. Our focus is to address the leading cause of Line of Duty Deaths since NFPA began tracking in 1979 – Heat Stress.
FABRIC TEAR TESTING
Fabric tear testing is designed to demonstrate the capacity of an outer shell to resist tearing once a rip or cut has occurred. A fabric with adequate tear strength will help keep that rip or cut from becoming larger and potentially compromising the safety of the PPE. Tear strength is tested by a machine that uses a piece of already cut fabric and measures the force it takes to rip the fabric along the initial cut.
Why is Tear Testing important for fire safety? Firefighters are often in situations where small cuts or tears in the outer shell can occur. Wearing fabric that tests poorly can lead to a shorter life-span for turnout gear, other garment failures and increased risk of burns.
TENSILE STRENGTH TESTING
Tensile strength testing is used to measure how much force it takes to pull a whole, uncut or untorn, fabric apart. It is an indicator of how well a garment will stay together when it has forces applied to it from a variety of situations.
In the chart, you will see tensile strength differences between a traditional Kevlar®/Nomex® blend and a typical, high strength blend. While the high strength blend shows visibly higher tensile strength numbers, the Kevlar®/Nomex® blend is the most popular fabric in the market and has been proven over the years to be one of the most durable products ever in the fire service.