Before any person enters a confined space, you must isolate any potentially hazardous services. Today we take a look at the two main methods of isolation.
The process by which an energy source is removed from service and employees are completely protected against the release of energy and material into the space, and contact with a physical hazard, by such means as:
- blanking or blinding
- misaligning or removing sections of lines, pipes, or ducts
- a double block and bleed system
- lock out or tag out of all sources of energy
- blocking or disconnecting all mechanical linkages
- placement of barriers to eliminate the potential for employee contact with a physical hazard.
Isolation from gases, liquids and other flowing materials
Confined spaces will often need to be isolated from ingress of substances that could pose a risk to those working within the space. Methods of isolation may include:
- complete disconnection of pipes or ducts
- insertion of blanks
- reliable valves that can be locked shut.
Disconnecting the confined space completely from every item of plant
This occurs either by removing a section of pipe or duct or by inserting blanks. If blanks are used, using the spectacle type with one lens solid and the other a ring will make checking easier. When disconnection cannot be done in this way, one alternative is a suitable, reliable valve that is locked shut, providing there is no possibility of it allowing anything to pass through when locked, or of being unlocked when people are inside the confined space.
Reliable valves that can be locked shut
Barriers, such as a single brick wall, a water seal, or shut-off valves (or those sealed with sand or loam to separate one section of plant from another), are sometimes present at a confined space and offer some degree of isolation of the space. However, these barriers are usually provided for normal working and may not provide the level of safety protection necessary for the high risks often found in confined spaces. A more substantial means of isolation may therefore be needed.
Whatever means of isolation you choose to use, it needs to be tested to ensure it is suitably reliable. It is the responsibility of the supervisor to ensure that all necessary isolations have been made and are effective.
Isolation from mechanical and electrical equipment
Mechanical and electrical isolation of equipment is essential if it could otherwise operate, or be operated, inadvertently. It is the responsibility of the supervisor to ensure that all necessary mechanical and electrical isolations (including lock-off of isolation switches) have been made and are effective.
Some confined spaces contain electrical and mechanical equipment with power supplied from outside the space. Unless the risk assessment specifically enables the system of work to allow power to remain on, either for the purposes of the task being undertaken or as vital services (i.e. lighting, vital communications, firefighting, pumping where flooding is a risk, or cables distributing power to other areas), the power should be disconnected, separated from the equipment, and a check made to ensure isolation has been effective.
Isolation could include locking off the switch and formally securing the key in accordance with a permit-to-work, until it is no longer necessary to control access. Lock and tag systems can be useful here, where each operator has their own lock and key giving self-assurance of the inactivated mechanism or system. Check there is no stored energy of any kind left in the system that could activate the equipment inadvertently.