Safe Work Practices > Confined Space Entry / Transformer Vaults > Initial Inspection-Gas Testing & Temperature

Throughout the process of preparing a confined space for entry, the potential atmosphere in the space should be tested. Gas testing is sometimes difficult from outside the space when it has first been opened. Depending on the shape of the space, it may have to be entered to conduct the required gas tests.

•Shut off air movers at least 15 minutes before the initial test, allowing any gas released from sludge or scale to be detected.

•Gas testing should be conducted from the man way first, checking for heavier and lighter than air substances. Refer to the product's MSDS to know what to test for and their effects, relative weights, how to test, etc.

•Initial entry to perform gas tests will be made with supplied air breathing apparatus and watch person at the entry way if the potential for an IDLH (Immediately Dangerous to Life or Health) atmosphere exists or if entry will be made into liquid in sour service. Conduct gas tests always checking for lighter and heavier than air gases. Appropriate chemical resistant clothing, gloves, boots, eye and face protection should also be worn depending on the substances involved.

•Allowable gas limits for safe entry:

▪Oxygen 19.5 - 23 % by Volume

▪Flammable Gas 0% LEL Maximum

▪Hydrogen Sulphide 10 ppm Maximum

▪Other Toxic Gases As identified by the MSDS

▪Temperature 30o C Maximum

If these limits cannot be maintained, the space is to be considered IDLH - see sub-procedure.

•Inspect internals for liquids, scale and sludge. Determine what they are and whether they may release gases when disturbed. Can these materials be removed from outside the space. What additional precautions need to be taken while these materials are removed.

•Inspect for other physical hazards and consider the precautions required to control these, (i.e.: bumping, tripping, falling, structural integrity of metal, etc.). Erect scaffolding where required, do not have workers working off ladders, etc., especially in a confined space.

•Inspect for signs of pyrophoric material (will spontaneously combust when dry and exposed to oxygen), usually found only in sour service vessels. Pyrophoric materials will not pose a hazard if kept wet while removed.

•Consider whether continuous monitoring is required or if periodic monitoring will ensure worker safety. When work stops for more than a half hour, the space should be rechecked.