Not All Momentary Thermal Hazards Are Equal

One of the biggest mistakes made in the workplace is in believing that, because a garment is flame resistant, it must be safe for all hazards. This simply is not the case.

• By Bill Rieth
• Dec 01, 2016

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 that 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.

First let's look at two of the most common momentary thermal hazards in the workplace today, 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 3 seconds and having temperatures ranging from 1200˚ to 1900˚. Arc flash, on the other hand, has a duration that is defined in milliseconds. There are 60 milliseconds in a second, and an arc flash commonly lasts only 2 or 3 milliseconds. However, an arc flash can have temperatures up to 34,000˚. That's four times hotter than the surface of the sun.

Each hazard is violent in its aspects but, as you can see, they have very different protection needs. Because of this, it is extremely important to understand which hazard you are trying to protect the worker from and ensure the proper flame-resistant garments are selected.

To simplify things. we should step back and look at how clothing is identified as flame resistant. We need to understand that the standards for determining FR performance are not garment standards, meaning they are not testing garments at all. They are testing fabrics. That being said, we can look at FR fabrics as a tree.

Before ever a fabric can be called FR, it must pass a vertical flame test known as ASTM F6413. If a fabric passes this test, it is now able to be called flame-resistant fabric. By passing ASTM F6413 the fabric, which is flame resistant, becomes the trunk of the tree. The fabric can now be tested to each momentary thermal hazard such as flash fire, arc flash, firefighter bunker gear, wildland fire protection, etc. These hazards are the branches of the tree. Each has its own dangers and parameters, and each requires very specific types of protection from flame-resistant fabrics. In some cases, the standards require the fabric to be made into a garment and tested, and in other cases the standards require swatches of fabric be tested. It all depends on how to determine the level of protection needed for that hazard.

Once a fabric has passed or been given a rating, it can then be cut and sewn into garments and show the proper labeling to inform the workers they have selected the correct garment for the hazard they are protecting themselves from.

Unfortunately, due to a lack of understanding and misinterpretation of standards, improper selection of FR clothing is a common error in the industry. As an example, let’s look at the oil & gas industry. Most companies in this industry 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 tested to a test method known as ASTM F1930. In this test, an extra-large coverall is made out of an FR fabric, placed on a mannequin that has calorimeters on it, and is exposed to flame.

This test does not rate the fabric. After being exposed to the flame, data is collected from the mannequin and a body burn percentage is predicted. If the prediction is that less than 50 percent of the mannequin received second- and third-degree burns, the fabric passes. Again, there is no rating or level given; it either passes or it fails. By passing this test, the fabric then meets the requirements of NFPA 2112. A garment is made out of the fabric and "2112" is displayed on the garment to let the wearer know that it has passed this test and is designed to protect the worker in a flash fire hazard. However, these same companies that often are concerned only with flash fire protection require a "CAT 2" or "PPE 2" label on these garments as well, which has no relevance to flash fire at all.

A CAT 2 or PPE 2 is a label put on clothing that 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. This is not a pass or fail test. The fabric is given a rating known as Arc Thermal Performance Value (ATPV). The CAT 2 or PPE 2 comes from a section of the standard NFPA 70E, which identifies specific hazard levels for electrical workers and provides four levels of personal protective equipment (PPE). A PPE 2 level is generally considered to be the most common level. As a fail-safe, many companies in the electrical industry require their clothing to be a minimum of CAT 2 or PPE 2.

Another standard known as ASTM F1506 defines the labeling requirements for arc rated (AR) clothing. ASTM F1506 requires that certain information be included on the label placed inside the garment, including the ATPV rating of the fabric. This in turn lets the wearers know what rating their clothing has been given. Nowhere in this standard, or any other standard or regulation, does it require that CAT 2 or PPE 2, or any other level 2 designation, be put on the outside of a garment. But, because we have come to identify this label as a way of identifying safe FR clothing, many companies will not buy FR clothing if it does not have this somewhere on the garment.

In short, many companies, only concerned with flash fire protection, incorrectly assume the garment will only protect the worker if that garment has a CAT 2 or PPE 2 label and will not approve clothing that does not have a CAT 2 or PPE 2 rating, even though this label is for electrical arc flash protection and has nothing to do with flash fire. NFPA 2112 does not require a rating for clothing. Nor is there a "level 2" requirement anywhere in the standard. It does require that it passes ASTM F1930. Very few, if any, companies wishing to protect their workers from arc flash require "2112" identification. When they do require it, they are looking to protect their workers from both flash fire and arc flash. This type of clothing is known as dual hazard protection. In this case, the clothing or fabric has been tested to ASTM F1959 for arc rating and ASTM F1930 for flash fire to ensure the worker’s safety in either arc flash or flash fire hazards. This is completely different than selecting FR clothing, which is not tested to the hazard required as noted in this article.

One of the biggest mistakes made in the workplace is in believing that, because a garment is flame resistant, it must be safe for all hazards. This simply is not the case. In fact, selecting FR garments not designed for the correct hazard could expose the worker to greater injury. To avoid this, assess your workplace environment and identify which momentary thermal hazards exist. Remember, it is very possible to have multiple thermal hazards. Then only select clothing that has the proper testing and identification as required by the standards for each hazard.

This article originally appeared in the December 2016 issue of Occupational Health & Safety.