Tests may find faults

Whenever we carry out a test, we may find a fault, and we must be prepared for one. 

After changing a chlorine cylinder, two workers opened the valves to make sure there were no leaks on the connecting pipework. They did not expect to find any, so they did not wear air masks. Unfortunately there were some small leaks, and they were affected by the chlorine. 

The workers actions were not very logical. If they were sure there were no leaks, there was no need to test. If there was a need to test, then leaks were possible, and air masks should have been worn. 

Similarly, pressure tests (at pressures above design, as distinct from leak tests at design pressure) are intended to detect defects. Defects may be present—if we were sure there were no defects, we would not need to pressure-test—and therefore we must take suitable precautions. No one should be in a position where he or she may be injured if the vessel or pipework fails (see Section 19.2). 

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