Key steps to follow when you suspect a dangerous atmosphere.

Select the appropriate type of calibrated instruments for the hazards identified in the assessment.
You must understand the characteristics of the work area in order to choose the right instruments. Different types of confined spaces present different kinds of toxic gas hazards. There are hundreds of different toxic gases or vapours. You need a familiarity with the characteristics of the confined space in order to narrow down the possibilities and choose equipment.

****Important – Order of the Tests to be Conducted****

1. Test for oxygen levels – Save Levels between 19.5% and 23%. Levels below 19.5% is considered oxygen deficient. Levels above 23% is considered oxygen enriched and is considered a highly flammable or explosive environment.
2. Next test for Flammable Gases or Vapours – save entry means your results cannot exceed 10% of the lower explosive limit LEL.
3. Final test – test for toxic gases, vapours, VOC (Volatile Organic Compounds) – safe entry means the levels are below the acceptable permissible limits (PEL).                                                                         For example, if a propane heater is being used inside a confined space, then you need calibrated monitors capable of measuring oxygen levels, carbon monoxide, and combustible gases.
   Warning: Combustible gas detectors should not be used to assess toxic atmospheres. Most combustible gas detectors do not respond to low concentrations of gases. For example, H2S Hydrogen Sulphide is flammable from 4.3% to 44%. But it
   is immediately Dangerous to Life or Health (IDLH) at 100 parts per million (0.01%} and would not be detected at this concentration by most combustible gas detectors.
   Most other toxic gases that are also flammable are dangerous in
   concentrations well below the LEL.