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| Units for E and En in Clause D.7 https://brainfiller.com/arcflashforum/viewtopic.php?f=7&t=630 |
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| Author: | Vincent B. [ Fri Aug 21, 2009 9:31 am ] |
| Post subject: | Units for E and En in Clause D.7 |
To which extent does NFPA 70E-2009 quotes correctly IEEE 1584-2002 in its Annex D? I ask because the Annex says both En and E is in J/cm^2, while because of the 4.184 factor in equation D.7.3(c), I believe it is possible that En is in cal/cm^2 and E in J/cm^2. Can somebody add their word on this, preferably quoting/verifying from IEEE 1584-2002? |
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| Author: | Jim Phillips (brainfiller) [ Mon Aug 24, 2009 10:06 am ] |
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You are correct! Annex D of NFPA 70E has the wrong units for En  - it IS cal/cm^2. I am surprised this is still carried over into the 2009 edition. IEEE is required to use all metric so En in IEEE 1584 actually does not identify the units since it is not completely metric. It just uses the label "normalized incident energy". The units of Joules/cm^2 occurs AFTER you multiply by the conversion 4.184
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| Author: | Vincent B. [ Mon Aug 24, 2009 2:04 pm ] |
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So you multiply by 4.184 to get E in J/cm^2, then you divide by that same factor to choose your PPE in cal/cm^2. What a great way to have another Mars probe crash! At least, if you don't do the final conversion, you'll suit up too much, not too lightly. What a mess the opposite could bring up... |
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| Author: | chris kennedy [ Mon Aug 24, 2009 2:55 pm ] |
| Post subject: | |
brainfiller wrote: I am surprised this is still carried over into the 2009 edition.
Appears someone should bring this to the NFPA's attention. |
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| Author: | Jim Phillips (brainfiller) [ Mon Aug 24, 2009 3:14 pm ] |
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Vincent B. wrote: So you multiply by 4.184 then you divide by that same factor
Pretty amazing, I know.
--Chris K. yes it should be brought up. Conference Room 1 in the forum is where we have been attempting to hash out some language for proposals for the next edition of 70E. Guess we just got another one added to the pile. |
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