Layering FR Garments 101
Having a layered FR clothing system is a great way to achieve the ATPV cal rating for your specific requirements. This is especially true when a person does not want to wear bulky or loose fitting coveralls or if the coveralls themselves do not provide quite enough protection.
It is a misconception that you can just add up the ATPV cal rating of say the two types of fabric and that would be the combined arc rating. An example of this would be a Henley shirt and a coveralls over top. However there is the addition of the air between the fabrics that actually adds to the insulating factor so in most instances the rating is higher then just adding the two numbers together. However this is still not a 100% guarantee in determining the arc rating as the correct way to do this is to have the specific garments in question tested together in a testing facility such as Underwriters Laboratories.
Another question that we get a lot and I would like to clarify is that can a person wear undergarments that are non FR under their flame resistant apparel.
Well the answer is yes you can as long as it is non-melting like 100% cotton although the non FR fabric will not add any more arc protection. Fabric that can melt such as acetate, nylon, polyester, polypropylene, and spandex cannot be used in the layer closest to your skin because in the event of a flash fire or electric arc, some heat will inevitably pass through the outer layer of FR and cause the undergarment to melt if it is made from synthetic materials.
The problem that can occur with the non FR clothing is in the instance where the outer layer is not closed off properly as in the zipper being left open a little or buttons not done up properly. What can happen is that the heat source enters through an opening and ignites the non FR fabric.
So there really is no reason to wear a non FR undergarment unless you are already achieving the desired arc rating with the initial outer garment. There are many good products available made out of soft feeling fabric such as cotton that can be used and are as comfortable as any non FR fabric that might be used.
An example of this would be wearing a nice Henley style shirt like the one at this webpage Henley FR Shirt
along with a coverall such as this.
Terry Smeader
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Tags: arc rating, ATPV, FR, FR garments, layering FR clothing
