QDIS Blog

I have posted a spreadsheet which will help in the initial evaluation of explosive hazards for chemicals. Here is the page where it is located.

This is from a paper by E. S. Shanley and G. A. Melhem of Arthur D. Little, Inc., entitled “The Oxygen Balance Criterion For Thermal Hazards Assessment“. Originally published in Process Safety Progress Volume 14, Issue 1 , Pages 29 - 31 Published Online: 17 Jun 2004

Here is the equation:
Oxygen balance = [1600 * (2x + (y/2) - z)] / M

Where:

M = molecular weight
x = number of carbon atoms
y = number of hydrogen atoms
z = number of oxygen atoms
(other heteroatoms are ignored)

If M (oxygen balance) is between -80 to +120 then the hazard potential is high
If M is +240 to +120 or -160 to -80 then the hazard potential is medium
If M is > +240 or is < -160 then the hazard potential is low.

An example: anisole C7H8O1 MW: 108.14

oxygen balance = [1600 * (2 * 7 + ( 8 / 2 ) - 1 ] / 108.14
oxygen balance = [1600 * ( 14 + 4 - 1 ) ] / 108.14
oxygen balance = [1600 * 17 ] / 108.14
oxygen balance = 27200 / 108.14
oxygen balance = + 252 therefore it isn’t a thermal hazard since it is > +240

The spreadsheet allows you to enter the molecule’s molecular weight and number of carbons, hydrogens and oxygens in it and the spreadsheet will then calculate the oxygen balance and color code the result. Below is a screenshot.

If the number is medium the result cell turns yellow; if it is high, the cell will turn red. This gives a visual feedback in addition to the number itself.

This is by no means a substitute for actual testing, but can give you a rough idea of the potential explosive hazard. The authors state that it is conceptually flawed and often dangerously misleading as a guide to energy release in general since it is based on stoichimetery. To fully answer such questions, you need to use thermochemical and kinetic considerations.

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