This question was asked recently on Arcflashforum.com from an end user of FR clothing. I thought that it was a great question because it deals with high visibility (hi-vis) clothing and under layers, which are both often confusing topics.
Question: We are required to wear high visibility clothing in the plant due to forklift traffic. High Viz (sic) FR long sleeve category 2 shirts have been issued to us as well as a High viz category 2 hoodie sweatshirt. Where the problem exists is summertime. Without air conditioning in the plant, long sleeves can get rather hot. It has been proposed to wear short sleeve non-FR high viz shirts to perform duties that do not require the use of FR clothing and if a condition presents itself, where FR PPE is required, either our long sleeve high viz FR shirt or hoodie would be put on. The question I have is whether we would need to take the short sleeve shirt off or could we leave it on under our FR shirt. The short sleeve shirt in question is made of a 4.25 oz/yd2 100% polyester knit. Most panels/equipment we work in are category 0. I would say up to 90% however we do have category 2 and 3 panels.
Answer 1: Polyester is not a nonflammable natural fiber, and cannot be worn beneath arc rated clothing (FR is no longer the NFPA 70E term used). To be in compliance, you would need to wear a natural fiber, if not wearing something that is actually AR (arc rated).
Answer 2: You cannot allow the polyester to be worn UNDER an arc rated FR shirt. This will melt at a rather low temperature and cause burns. NFPA 70E does not allow polyester to be worn, even in blends. For the electrical workers, use an ANSI 107 hi-vis compliant material which also meets ASTM F1506. There are many t-shirts, vests (even mesh vests) which meet this standard. I recommend a t-shirt since it will be cool all the time and never ignite or melt, then add the long sleeved shirt for energized work. Thus you’ll be creating a safe working condition and you will have extra protection under the AR shirt. The t-shirt doesn’t have to have any specific rating – just be sure it has a rating; you can’t count it as official extra protection unless the system is rated.
Comment: One thing to note is, if your work site requires hi-vis, neither FR or non-FR cotton has the ability to meet the ANSI 107 hi-vis requirements. That means the hi-vis short sleeve t-shirts would have to be some sort of FR modacrylic blend, with an arc rating, which can be dyed to meet the hi-vis requirements. If they’re just worried about wearing a t-shirt (not hi-vis) under their FR, that shirt would need to be of natural fibers like 100% cotton.
If there are any more specific questions regarding high visibility and flame-resistant clothing requirements, please feel free to email me at email@example.com