MIL-STD-810 Explosion Proof for Class 1 Div. 1? 1

[PW2006]

We are considering a instrument that has been certified for MIL-STD-810 Explosion Proof. But I wonder if this means that it can be used in Class 1 Div. 1 or Div. 2 area. Is there any special concern? Does it still need a separate certificate even if it is OK to be used?

Thanks.

 

[eadwine]

Have you thought of checking with the vendor? They should be able to tell you whether or not the instrument has been cleared for use in the appropiate Class and Division Area and provide Cert's. to that effect.

 

[bchoate]

PW2006
Eadwine's advice is good for a true picture of what the instrument is rated for. But, it is unlikely that the instrument you mention will be acceptable and this is why;

The instrument of interest is rated as explosion proof IAW MIL-STD-810F. This means the instrument was tested (1)under normal operating conditions to determine if such operation can ignite a test mixture and (2) a case test to test whether the case can contain an explosion if such occcured. Test conditions for Method 511.4 are based on N-hexane as the ignitable material at a 3.82% v/v concentration in air at controlled temperature and altitude relative to sea level. Material of concern is JP-4.

The instrument is tested in normal operation and rated as 'intrinsically safe' if it passes the tests. It is a given that an instrument (e.g. thermocouple) can be intrinsically safe in the normal mode operation but become unsafe by a fault mode in any connected equipment (recorder). The instrument is intrinsically safe in a N-hexane/air ignitable mix (no electrical discharge above the MIE of hexane (.29 mJ) or hotspot temperatures above the AIT of hexane (223 C).

The target area classification for the instrument is Class 1, Div 1 or 2. Specification should be expanded to group level. MIE's for hydrogen and acetylene are 0.017 mJ. The instrument wouldn't be acceptable in those groups. The instrument is rated IAW MIL-STD-810F. Unless the manufacturer has dual certifications to include appropriate agency hazard area rating for intrinsic safety, the MIl-STD-810F rating is probably not enough.
See:

http://www.scribd.com/doc/2082009/Rugged-Notebooks-810FExplosive-Atmosphere-Test-Methods

 

[PW2006]

Thank you for your fast reply. I already asked the manufacturer before I posted this question. The guy in the instrument manufacturer told me that it would be OK. But I was not sure. I will go back to him and ask for more proof or explanation.

I will post more after I find more answers from the manufacturer.

Thank you again.

 

[bchoate]

PW2006
Note: You can probably use the instrument. MIL-STD-810f Method 511.4 provides two testing protocols. The first tests whether an instrument can generate sufficient spark energy or spot temperatures to ignite a test mixture. This is a measure of intrinsic safety for the instrument. Test two tests whether the case can contain the ignition of a test mixture without igniting the same mix surrounding the cased instrument. This is an explosion proof measure.

The standard test vapor is N-hexane. This material provides certification for Class 1, Div 1/2, Group D. The temperature rating is T2D. Unless the ignitable vapor(s) in your application are group D or higher there still may be questions. The explosion proof test with N-hexane may hold for A, B, or C materials or it may not. The best check is for MIL-STD-810f run with an appropriate test gas. This is permitted under the STD protocols.

MIL-STD-810f isn't exactly FM or CSA certification. In the final analysis, what matters is what the vendor will document and what the insurance underwriter will accept for your application.