i am brand new to the arc flash ppe seen and i have a few questions.

question 1
if i am wearing an fr shirt that is rated at 8.5 cal and an fr pant that is rated at 10.5 cal with no nm cloths underneath am i hrc2 compliant?

question 2
if i am wearing the same clothes as aboove and i put on a 20 cal pair of coveralls am i hrc3 compliant?

asume that i know to wear glasses, gloves, leather boots, etc.....

question 1
if i am wearing an fr shirt that is rated at 8.5 cal and an fr pant that is rated at 10.5 cal with no nm cloths underneath am i hrc2 compliant?

Yes, you are Level 2 compliant for clothing, with the exception that Level 2 also requires an Arc Rated Full Face Shield. Your total IE rating is 8.5 cals, the lower of the two garments, but above 8.0 cals you would need the Level 3 bee keepers hood. 2* would require a banaclava sock hood or a Level 3 bee keepers hood.

question 2
if i am wearing the same clothes as aboove and i put on a 20 cal pair of coveralls am i hrc3 compliant?

No, Level 3 is 25 cal. The clothing layering is not cumulative. The reason for this is that the clothing, in addition to it thermal ability, must be able to handle the pressure wave associated with with cal rating. So the 20 cal suit can not thermally, or mechanically, handle a 25 cal blast. Since it can be physically damaged, ie torn apart, by a 25 cal blast it would expose the lower rated garments underneath. The outer layer is the layer that has to match the incident energy. But layering a level 1 or 2 clothing as a base layer, and then donning a level 3 suit over it, does afford you greater protection. Depending on the level 3 suit, level 1 undergarments may be a requirement. The NFPA table cites FR garments as being required under the suit, but some manufacturers are getting there rating on the suit itself without added layering, in which the suit alone provides the rating.

thank you haze10
so if i understand you correctly if my work uniform consists of an 8.5 cal shirt and 10.5 cal pant and i put on a pair of 25 cal coveralls i wourl be hrc3 compliant. and if i put on a 40 cal protection suit i would be hrc 4 compliant.

asume that i am useing proper face shilds and ear plugs and gloves and leather boots.

Check with the PPE manufacturers also. Often the sum of the FR ratings is greater thant the individual ratings. i.e. 8.5 pants and 20 coveralls might equal something higher thn 28.5. The manufacturer should be able to tell you what the higher rating is. It is becuase you have an air gap between the layers that adds insulation.

Gotta disagree with you here Haze, the layers are additive as proven during testing, I dont have the reference off the top of my head but I think that it is discussed somewhere in ASTM F 1959. Also annex H (I know, not really part of the 70E, but just another reference) discusses using 25 cal coveralls over NM fabrics to acheive HRC 4 protection.

I was told by a rep from Oberon that when they send the clothing out for testing there is also some type of test that guarantees the fabric will not tear or open. I agree with you about layers adding thermal protection. But if they are blasted off because the pressure wave is greater than the fabric is designed to withstand, it doesn't work as a system. If you have some references I will check them out, but I don't remember seeing any cumulative effect being mentioned in Art 130.