Where maintenance requires that normal guarding is removed, or access is required inside existing guarding, then additional measures are needed to prevent danger from the mechanical, electrical and other hazards that may be exposed. There should be clear company rules on what isolation procedures are required, and in what circumstances (for example, some cleaning of mixing machinery may require isolation, even though it might not be considered a maintenance task).
The basic rules, however, are that there should be isolation from the power source (usually, but not exclusively, electrical energy), the isolator should be locked in position (for example by a padlock), and a sign should be used to indicate that maintenance work is in progress. Isolation requires use of devices that are specifically designed for this purpose; not devices such as key-lockable emergency stops or other types of switches that may be fitted to the machine. Any stored energy (hydraulic or pneumatic power, for instance) should also be dissipated before the work starts.
If more than one maintenance worker is involved in the work, each of them should lock off the power with their own padlock. Multi-padlock hasps can be used in such circumstances. Such isolation procedures can also be applied to locking off valves for services (such as steam) and material supplies.
Before entering or working on the equipment, it is essential that the effectiveness of the isolation is verified by a suitably competent person.
A 'permit to work' is a formal, written, safe system of work to control potentially hazardous activities. The permit details the work to be done and the precautions to be taken (for instance, they may involve limiting the movement of overhead cranes, the precautions needed for high voltage work or they might detail rescue arrangements for certain types of work). Permits should be issued, checked and signed off as being completed by someone competent to do so, and who is not involved in undertaking the work.
Permits to work will tend to be appropriate in the following types of situation: where contractor's work interfaces with normal production activities; work on plant which must be isolated from the possible entry of fumes, liquids, steam or gases (included those from fire extinguishant systems); hot work which could cause fire or explosion, and entry into vessels, machines or confined spaces.
A 'confined space' is a place which is substantially (though not always entirely) enclosed, and where there is a risk of death or serious injury from hazardous substances or dangerous conditions (such as a lack of oxygen).These can include storage tanks, silos, reaction vessels, enclosed drains and sewers, open topped chambers, ductwork and poorly ventilated rooms.
Confined spaces are often doubly dangerous, and have regularly killed not only the first person - who is overcome by the fumes (or lack of oxygen) - but also a second or third person who have attempted a rescue without the proper equipment. HSE has produced a 7 page guide to confined spaces, specifically written for small firms, to guide you through the requirements of the Confined Spaces Regulations 1997: