MIE to MIC conversion - instrinsically safe 2

[zappedagain]

I have a circuit that can generate a 0.13mJ spark, well below the minimum ignition energy (MIE) of methane (0.28mJ).

I want to see if this circuit is intrinsically safe for a Class 1 Div 1 Group D environment with a minimum ignition current ratio (MIC) spec of 0.8.

What to I need to convert between MIE and MIC?

Thanks,

John D

 

[7anoter4]

MIE=L*MIC^2/2 for Low Voltage and MIE= k * p *d^3 for High Voltage.
Where p =the initial pressure of the mixture[kg/cm^2]
d=the quenching distance[m]
L= circuit inductance in Henry.
See:

http://www.combustion.org.uk/ECM_2009/P810126.pdf

NFPA 493-1975 considered only the energy accumulated in inductance L. Actually, the ignition energy may be accumulated in capacitive and in resistive only circuitry. See:

http://www.am.pepperl-fuchs.com/pdf/documents/eg06_p007-96_engineer_guide.pdf

A quotation from "Instrument Engineer's Handbook page 884 "Energy Levels":
Curves such Fig. 7.2 g [from NFPA 493-78] show limiting circuit parameters that provide ignition energy for a particular gas. They can be used safely only after careful examination of specific equipment by ONE SKILLED IN THE ART and by application of an adequate safely factor. Actual ignition testing of the specific apparatus is the preferred practice".
In USA for example you may call to UL or Factory Mutual.

 

[zappedagain]

Thanks 7anoter4,

Those references are excellent! That's a star for you!

John D