“Current State of FR Clothing” is a quick overview of some important parts of the need for arc rated clothing. I prefer not to use “FR” and try to stop myself since it isn’t clearly defined other than in the proper standards. “FR” is a very generic term. Use arc rated for clothing meeting ASTM F1506 for clothing in arc flash, F1891 for rainwear in arc flash. In flash fire use NFPA 2112 for clothing in flash fire and ASTM F2733.
One item could be clarified, one MAY test layers and use layering for protection (this is recommended by arc flash clothing experts) so you DO NOT have to have the OUTER LAYER rated for the whole hazard. >25 cal or so this is impossible but IF you do not have a rating on the system officially you can only count one layer. I recommend getting with the manufacturers to see if they have data.
Brian was correctly trying to let folks know they couldn’t just add up ATPV levels to get the system protection. The ASTM F18 committee is working on simpler ways to look at protection. Wearing 2 layers of arc-rated clothing WILL be more protective in MOST cases but sometimes you will not get added protection in the DIRECT arc flash area. Note arc flashes are focused events so one area of the body gets more energy than the rest of the body.
Another point of misunderstanding in the article is the implication that if you have 9.1 cal/cm2 exposure you must don an HRC 3 suit (25 cal/cm2 protection). This is incorrect. HRC is related to the hazard/risk assessment in the NFPA 70E tables and should not be confused with calculations. If you have calculations you must protect to the calculations and are not required or allowed to mix in the tables or HRC’s. The HRC levels may be useful but they are not mandatory unless you use the tables.
For example. If you have a 9 cal exposure you must use the ANNEX F in NFPA 70E to do a RISK assessment. The risk assessment might determine that you wear less PPE than 9 cal based on HOW the job is done, the likelyhood of any arc in the particular work practice you are involved in but in most cases the company chooses to protect to 9 or 10 cal but you are not forced to protect to 25 cal/cm2. One good thing to do is to look at what parts of the body are likely to receive this amount of energy and focus efforts there, hands, arms and face are the most likely to recieve energy.
So provide arc rated clothing to the hazard and think of what other body parts need protection. Note AF calculations are often done at 18 inches away from the arc. If body parts are closer to the hazard, they may need more protection. Some rubber gloves with leather protectors have been shown to protect to more than 100 cal/cm2 but others will ignite at 15 cal/cm2. The end user doesn’t know this yet because we haven’t got the glove standard through ASTM F18 yet. This is likely in May 2011.