Cable confined space

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 use of TRDs has been facilitated by the use of fibre-optic cable assemblies (Section 6.12.4). This permits sensing in confined spaces as well as enabling the sensor to see round corners and into regions containing nuclear or electromagnetic radiation 36 . Low levels of source visibility can be overcome by employing two-colour or ratio sensors which measure radiation at two different wavelengths simultaneously. Such instruments can be used where dust or dirt obscures the source from the sensor. 

This method of stress measurement is not often used today, because it is slower and less precise than the diffractometer method. However, the photographic method still has some advantages. The required apparatus is very simple a small back-reflection camera fixed to the head of a shockproof x-ray tube energized through a shockproof cable. This apparatus is smaller, lighter, more robust, and much cheaper than a mobile diffractometer. It is also more mobile and better suited to work in a confined space. 

In my experience, electricians spend a lot of time on their knees in confined spaces because many electrical cable systems run out of sight away from public areas of a building. 

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