Not All Momentary Thermal Hazards Are Equal

There is a strong misconception in the workplace that all flame resistant (FR) clothing is designed for all momentary thermal hazards. A momentary thermal hazard is an event which includes some type of heat or flame lasting for a short duration of time. Each momentary thermal hazard has its own characteristics and, therefore, requires specific protection needs from FR clothing to protect the worker.

The two most common momentary thermal hazards in the workplace today are arc flash and flash fire. These two hazards are vastly different in duration and temperature. Flash fire is defined in NFPA 2112 as a fast moving wall of flame lasting up to three seconds and having temperatures ranging from 1200˚ to 1900˚. Appropriate FR protective clothing should display 2112.

Arc flash has a duration that commonly lasts only two or three milliseconds, but with temperatures up to 34,000˚ – four times hotter than the surface of the sun! While not mandatory, appropriate FR protective clothing will indicate, at a minimum, CAT2 or PPE2 on the outside of an arc-rated garment. The required internal label will provide more detailed information.

Each hazard is violent in its own aspect and each has very different protection needs. Becauseof this, it is extremely important to understand which hazard you are trying to protect your worker from and ensure the proper FR garments are selected.

The standards used to determine FR performance are not garment standards, which means the garments are not being tested; the fabric is. A fabric is labeled FR if it passes a vertical flame test known as ASTM F6413. Visualize this FR fabric as a tree. By passing ASTM F6413, the fabric becomes the trunk of the tree and can now be subjected to additional momentary thermal hazard testing such as flash fire, arc flash, fire fighter bunker gear, wild land fire protection, etc. These subsequent hazard tests can be considered the branches of the tree. Each has its own dangers and parameters and each requires very specific protection from FR fabrics. In some cases, standards require the fabric be made into a garment before testing and in other cases, standards require swatches of fabric be tested. Once a fabric has passed required testing, or been given a rating, it is cut and sewn into garments that are labeled to indicate which potential hazards it is designed to protect workers from.

Unfortunately, due to a lack of understanding and misinterpretation of standards, improper selection of FR clothing is common. In the Oil & Gas industry, most companies are concerned with meeting the OSHA requirements for FR clothing worn in an environment where flash fire is a known hazard in order to protect their employees. This hazard requires that fabric be subjected to a test method known as ASTM F1930. In this test, an extra-large coverall made of the FR fabric is placed on a calorimeter-equipped mannequin and exposed to flame. Rather than rating the fabric, this test collects the data from the mannequin post-burn and a body burn percentage is predicted. A “pass” for this test is a prediction of 2nd and 3rd degree burns to less than 50% of the mannequin’s surface. This is a pass/fail test. There is no rating or level given. A passing grade means the fabric meets the requirements of NFPA 2112. A garment made out of the fabric has “2112” displayed on it to let the wearer know that it is in compliance with requirements and is designed to protect the worker in a flash fire hazard.

Other garment testing labels often required, such as CAT2 or PPE2, have no relevance to flash fire at all. A CAT2 or PPE2 label on clothing indicates it has been arc-rated using a test method known as ASTM F1959 and is designed for protecting workers in an electrical arc flash. The test requires swatches of fabric to be exposed to different levels of incident energy. Rather than a simple pass/ fail, the fabric is given an Arc Thermal Performance Value (ATPV). The NFPA
70E Standard identifies specific hazard levels for electrical workers and provides four levels of personal protective equipment (PPE). A PPE2 level is generally considered to be the most common level. As a failsafe, many companies in the electrical industry require their clothing to be a minimum of CAT2 or PPE2.

Another Standard, ASTM F1506, defines the labeling requirements for arc-rated (AR) clothing and requires certain information be included on the label placed inside the garment (including the ATPV rating of the fabric) to inform the wearer of the rating the clothing has earned.

No standard or regulation actually requires a CAT2 or PPE2 designation, but since this designation has become synonymous with safe FR clothing, many companies will not buy FR clothing that does not display this rating somewhere on the garment.

One of the biggest errors made when choosing FR clothing is the idea that because a garment is flame resistant, it is safe for all hazards. This simply is not true. Selecting FR garments not designed for the correct hazard could expose the worker to greater injury. Each workplace environment should be assessed and momentary thermal hazards that exist should be identified (it is very possible to have multiple thermal hazards). FR clothing should then be selected that offers the proper testing and identification as required by the standards for each hazard identified.

Bill Rieth is Director, Business Development for Justin Flame Resistant Apparel division of Fechheimer. He can be reached at

Bill Rieth


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