Before the space is entered it should be thoroughly ventilated. Effective ventilation capacity is also dependent upon the size and position of openings to the space. Well placed openings improve the flow of air and will help ensure that all areas within the space are effectively ventilated.
Once the space has been ventilated, the atmosphere should be checked using a suitable instrument(s) to test for oxygen, flammable gases or vapours, carbon monoxide, hydrogen sulphide and other toxic gases as appropriate:
- The oxygen content should be measured and a nominal reading of 21 % achieved. Any space with an atmosphere having less than 21 % oxygen by volume should NOT be entered until the reason for the low oxygen level has been established and resolved;
- Flammable vapours should be measured with a suitably sensitive combustible gas detector. The concentration of flammable vapour must be below 1 % of the Lower Flammable Limit (LFL) before entry can proceed; and
- A toxic gas detector should be used to ensure that the levels of toxic gases are within the required safe Threshold limit Value (TLV).