Disposable Secondary FR Garments: What Really Matters When Selecting a Garment
Clearly, the addition of a flash fire or flame hazard to a scenario involving dry or liquid chemicals can significantly complicate protection.
Most of our standards and test methods for flash fire and barrier/chemical protection deal with these two hazards discretely, as if they occurred in a vacuum. It is little wonder, then, that end users and many manufacturers tend to evaluate garment performance against these hazards in the same manner. Unfortunately, designing garments for use in multi-hazard environments, especially where flash fire or flame is concerned, is not quite so simple. An event where both hazards, flash fire and chemicals, are encountered simultaneously can have a drastically different result for the end user than if the hazards were encountered individually. The use of disposable garments over thermally protective garments (TPGs) is a classic example.
As the use of thermally protective garments increases around the world, so too does the need for disposable protective garments to be worn over them. Also increasing is the selection of products that claim to be suitable for this application and, subsequently, confusion over which disposable garment to choose.
These garments are commonly referred to as Disposable Secondary FR Garments because they are intended to provide barrier protection to the wearer without compromising the protection afforded them by the TPGs worn underneath. Once again, these garments are intended to provide the complete barrier protection the wearer requires, but they do not provide thermal protection unless worn over TPGs. While conceptually this is relatively straightforward and understood by most, applying it to the decision-making process is not so simple because of our predilection for considering hazards individually rather than collectively.
There are numerous test methods and standards on flame resistance and thermal protection, but none of them is written specifically for disposable secondary FR garments. Some certainly have application, but these standards and test methods focus on TPGs or on characterizing the flammability of a fabric. Further complicating this issue are some manufacturers who cite a standard that was changed in 1996 and is no longer applicable to protective clothing. As a result, many end users and even some manufacturers get "wrapped around the axle" over the FR testing of disposable secondary FR garments to the exclusion of all other testing. This is unfortunate and unnecessary if one takes the time to consider the disposable secondary garment’s function in the ensemble.
Disposable secondary FR garments differ from most disposable protective garments in that they are multi-hazard garments. As such, evaluation of these garments based on performance against any single hazard can be terribly misleading. Garments intended to be worn as a part of a more complex ensemble should be tested as they will be worn and challenged with the hazards as they may be encountered in the workplace.
As an example of how testing against individual hazards can be misleading, consider a spunbond meltblown spunbond (SMS) polypropylene fabric or a hydroentangled (spunlaced) woodpulp/polyester disposable fabric that is treated with flame-retardant chemistry and sewn into garments. Either of these garments may achieve the flame resistance necessary to meet a simple FR standard or test method such as ASTM D6413. Both of these products are also capable of performing reasonably well in terms of dry particle barrier protection, but what about liquid barrier?
If these two garments do not have some chemical treatment to enhance their repellency, the wearer may unwittingly be at risk. SMS can provide adequate barrier to water and some light sprays of liquid chemicals, as evidenced by its ability to attain CE Type 6 classification. But what happens when polypropylene SMS is exposed to a common workplace liquid such as oil, grease, hydraulic fluid, or solvent? The answer is that it absorbs these liquids. This characteristic of polypropylene is why it is commonly used in oil skimming booms to contain oil spills. It absorbs oil and repels water. The result would be the outer garment of the wearer’s ensemble becoming a reservoir for flammable liquid, holding that fuel in close proximity to the TPG worn underneath it. In case of saturation, the SMS garment may even act as a "wick," transferring the liquid fuel into the structure of the TPG underneath it, compromising the thermal protection otherwise provided by the TPG.
The same is true for garments made of hydroentangled woodpulp/polyester fabric. The woodpulp component of these fabrics is typically 55 percent by weight. Why is this important? Well, the woodpulp in the fabric, unless treated for repellency, will act just like a paper towel, absorbing most liquids--especially oil, hydraulic fluid, or solvents--that may contact it. In such cases the woodpulp, just like the polypropylene SMS above, will become a fuel reservoir and a conduit for the transfer of fuel into the structure of the TPG underneath, with the same resultant loss of protection to the wearer.
Establishing a Protection Hierarchy
Clearly, the addition of a flash fire or flame hazard to a scenario involving dry or liquid chemicals can significantly complicate protection. In the case above, the inclusion of flash fire or flame along with exposure to something as common and innocuous as oil or hydraulic fluid highlights the hazard posed by the flammability of these liquids. This hypothesis is supported in modified (vertical orientation) TPP testing using a copper calorimeter and flame impingement on combined TPG and disposable secondary FR garment samples that have been exposed to as little as 10 ml of oil. (See photos 2 & 3.) The test resulted in heat transfer through the test samples that far exceeded the clean samples of the TPG by itself. This result shows that the combination of disposable secondary FR garments that lack additional barrier protection and flammable liquids may act to compromise the thermal protection of the TPG it is worn over.
Given that current test methods and standards address hazards individually, how then should disposable secondary FR garments be evaluated? The process begins with a detailed job safety analysis that includes consideration for multiple-hazard environments and the impact that each of the hazards may have on other elements of the environment, including those that may not necessarily be deemed a hazard otherwise. A significant component of this analysis should be the establishment of a protection hierarchy for the hazards present.
In the case of disposable secondary FR garments, we have previously established that these garments are intended to provide the complete barrier protection needed by the wearer but not, by themselves, provide the wearer with adequate thermal protection. This statement establishes the hierarchy for the hazards for which these garments offer protection. You are wearing disposable secondary FR garments for their barrier properties, not their FR capability. For thermal protection, you have a TPG on underneath the disposable. Even the name "disposable secondary FR garment" alludes to the relative importance of barrier and FR protection. In short, why are you wearing a disposable secondary FR garment over TPGs? The answer is because the TPG fails to provide protection against some hazard that the disposable garment does. Therefore, barrier is the primary function of the disposable, provided it does not prevent or compromise the protection offered by the TPG. Focusing the flame resistance of disposable secondary FR garments in the selection process ignores the primary reason for wearing the garment.
To effectively evaluate the performance of disposable secondary FR garments, end users first need to determine whether the garment provides the barrier or other protection that is not provided by the TPG and secondly that the disposable secondary FR garment will not compromise the protection offered by the TPG if subjected to a multi-hazard event. To accomplish this, testing of these garments should hinge on testing the ensemble, both the disposable secondary FR garment and the TPG, for repellency using a flammable liquid such as oil or hydraulic fluid and then subjecting the exposed samples to flammability testing that will quantify heat transfer through the ensemble to the wearer. This two-step process will characterize the performance of the each layer, as well as the total ensemble, in terms of barrier to commonly encountered flammable liquids and provide detailed information on the thermal protection offered by the ensemble when exposed to both hazards simultaneously.
ISO 6530, commonly referred to as "The Gutter Test," allows for the evaluation of multi-layer garments or ensembles against exposure to 10 ml of liquid over a 10-second period of time while the fabric sample is positioned at a 45-degree angle. (See photo 1 at the start of this article.) This is not unlike exposures that may be encountered in the workplace. Individual ensemble layers can then be weighed to determine the effectiveness of the barrier offered by the ensemble.
Once barrier has been determined, the same barrier test samples should be tested for thermal protective capability. For this, we recommend a modified TPP test using a copper calorimeter to measure the heat transfer through the entire ensemble. By comparing the total calories of heat energy that passes through the ensemble samples, a good relative comparison of the effectiveness of the ensemble can be made. By testing a clean sample of the TPG using the same modified TPP test, a relative comparison can be made to the ensemble samples that were exposed to liquids and a determination can be made as to whether or not the disposable secondary FR garment, combined with a flammable liquid, will compromise the protection that the TPG alone is capable of offering. As an added benefit, this test protocol also can be used to evaluate barrier and effect on thermal performance for specific chemicals, for specific TPGs, or both.
Selecting the appropriate disposable for use over thermally protective garments does not have to be difficult, provided that you first consider what the garment must do, consider multiple hazards in conducting your job safety analysis, and ask the for data that is relative to how the garment will be used.
This article originally appeared in the March 2015 issue of Occupational Health & Safety.