Flame Resistant, Flame Retardants, Rated Materials and Garments: What’s the Difference?

In terms of Personal Protective Equipment (PPE), what is the difference between Flame Resistance, Flame Retardants and “Rated” materials and garments? These are words commonly seen in the industrial AR and FR market–so what do they mean, and what hazard can you expect “flame resistant” clothing to protect from?

Defining the Terms

Flame Resistance– “The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or nonflaming source of ignition, with or without subsequent removal of the ignition source.” (NFPA 2112, ASTM D123, etc.)

Flame retardant– According to ASTM D123 Standard Terminology Relating to Textiles, flame retardant is defined only as ” a chemical used to impart flame resistance”.  Flame resistance is a vague term unless it’s used in conjunction with a standard so that users can make informed decisions about what hazard the product is or is not appropriate for. A flame retardant treated fabric is a fabric which has been treated with a chemical or chemicals to impart flame resistance but may or may not be “flame resistant” by any known standard.

Arc, Flame or Firefighting Rated ­– The term “rated” was originally adopted for arc flash exposures and used in ASTM F1506 to refer to materials which had been rated for a level of protection from an arc flash hazard versus simply claiming it met a small scale standard test criteria.  As it’s used today, “rated” means the material or fabric meets a full battery of flame tests and receives ongoing testing which a consensus standard committee has deemed to be adequate for PPE for a particular hazard like arc flash, flash fire or structural and proximity fires.  These garments may not totally protect a worker from every exposure, but they have a known level of protection to a specific exposure, usually by testing to a full scale test, which is more predictive of the actual performance in the hazard.

While the differences in these definitions appear to be simple on the surface,  it can become quite complicated for end users…especially when marketing terms are thrown into the mix. Fortunately, we do have standards and specifications that can help to further define the terms.

The Real-Life Issues

Critical issues include identifying the proper type of flame resistance needed for the worker’s hazard (commonly known as the “rating”) and the durability of the flame resistance (especially if it is a flame retardant treated fabric).   Do not make the mistake of assuming that all flame-retardant-treated fabrics are bad; quite the contrary–these are some of the best materials on the market for certain hazards.  Arguments can be made for the cost of the garment and cost per wearing, but either an inherently-flame-resistant material (the chemical structure of the fibers in these fabrics make them flame resistant and this resistance cannot be washed out) or a flame-retardant-treated material (these can be wear-life-dated, such as 25 or 50 washes, or durable for garment life which is almost always the best choice) can provide a level of flame resistance and rated protection appropriate for the hazard.

From the 1950s until the 1990s, flame resistance was generally determined by three primary tests:

  1. Vertical flame test (the most common bench test to measure flame resistance in textiles)
    [ASTM D6413]. This test is small-scale, inexpensive and only used as a beginning test or control test.  It has NO correlation to protection values.
  2. Thermal protective performance (TPP), which has some basic correlation to protection values.
    [NFPA 1971, Protective Clothing for Structural Fire Fighting]
  3. Oven Testing, known as Heat and Thermal Shrinkage [NFPA 1971, NFPA 2112, and others].

The vertical flame test was developed when there were very few fabric options on the market.  Before long, new fabrics were developed which could pass the vertical flame test, but the fabrics were not actually protective in most hazards because of their propensity to melt and drip during a real exposure.  As a result, other tests were developed to better screen products.  The TPP tests for thermal protective performance from flame and infrared radiation from a lamp and gives a time to predicted burn using the Stoll curve criteria as a simple model of burn prediction.  The heat and thermal shrinkage test was designed to expose certain materials which could pass the other tests but might cause a garment to shrink so much that the garment would not cover the skin.  The method also rules out thermoplastics that would melt and drip at 500 degrees F.  Oven shrinkage is not used in arc rated garments since the full scale arc flash test concurrently exposes issues with shrinkage that will affect a wearer as well as melt and drip hazards.

Rating of Fabrics & Garments

We recommend using rated fabrics versus those with claims of generic flame resistance by citing obsolete or inappropriate standards (see below).  Following a full standard specification (such as ASTM F1506 or NFPA 2112) which uses a battery of tests, and most often includes a large scale test  similar to the actual exposure, will provide for more adequate protection than a single small scale test.

Vertical flame tests allow many materials to pass which do not protect in arc, flash fire, firefighting etc.  Passing vertical flame criteria alone has NO support in the US, the EU or any other developed country for textiles used in these hazardous environments. Today we continue to use the term “flame resistant”, but we must specify a standard for worker protection rather than just a test which may or may not reflect the performance of the material in an actual thermal hazard.

To identify the proper “flame resistant” material for end-use, the following must be done:

  1. Assess the hazard or hazards in your work environment:  arc flash, flash fire, structural firefighting, wildland firefighting, chemical exposures or a multi-threat environment involving other hazards.
  2. Work to engineer out the hazard or minimize it by some administrative or engineering mitigation.
  3. Use the proper standard for your hazards or find a compromise if the standards conflict.
  4. Assess the job situation to see if the PPE required is adequate, but not overly restrictive.

The most common flame resistant hazard based rating standards are the following:

Standards commonly misused to claim generic flame resistance on PPE garment labels are:

  • NFPA 701 (textiles for buildings, not garments).
  • ASTM D6413 (test method commonly used but which has no pass/fail criteria).  Never use a garment labeled with only this standard; it is only a test method and the data provided by it is of little use without further testing.
  • Federal Test Method Standards (FTMS) 191A-5901 or FTMS 191A-5903.  These are old versions of ASTM D6413 which are no longer published since they do not provide adequate flame resistance alone.

Leave a Reply