Vessels not isolated from sources of danger

Before entry is allowed into a vessel or other confined space, the vessel should be isolated from sources of hazardous material by slip-plating or physically disconnecting all pipelines and by isolating all supplies of electricity, preferably by disconnecting the cables. On the whole, these precautions seem to be followed. Accidents as the result of a failure to isolate are less common than those resulting from a failure to remove hazardous materials or from their deliberate reintroduction as described in Sections 11.1 and 11.2. However, the following are typical of the accidents that have occurred. 

The manhole was smaller than those used today, and if the men had been overcome, rescue would have been difficult. Before 

The blowdown valves on the boilers were operated by a special key, which had a lug on it so that it could not be removed when the valve was open. It was therefore impossible, in theory, for two blowdown valves to be open at the same time. However, the boiler fitter kept and jealously guarded a private key w ithout a lug and had used this one to open the blowdown valve on the boiler that was under repair. He forgot to tell the process foreman what he had done or to close the valve. The presence of this key would appear to have been of little moment as long as the correct procedure of complete isolation was maintained, but as soon as it was departed from, the additional key became a menace, which eventually enabled the present tragedy to occur, the accident report said. 

Any system based on the use of a single key is error prone, as it is so easy to acquire a spare. 

Checking the starter before working on electric equipment is a useful final check that should always be made, but it does not prove that the equipment has been isolated there may be an interruption in the power supply. 

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