Before an employee enters the space, the internal atmosphere shall be tested, with a calibrated direct-reading instrument, for oxygen content, for flammable gases and vapors, and for potential toxic air contaminants, in that order.
We test for oxygen before testing for flammability (LEL) for two (2) critical reasons:
- One is a technological limitation of the equipment, and
- The other is an immediate life-safety priority
Here is the breakdown of why this sequence is mandatory in confined space entry and industrial hygiene.