When operating in a confined space, the ingress of gas, liquids or flowing materials will affect the environment, which may become hazardous to those inside the confined space.
Personnel should be aware of the environment and any associated processes that may affect the confined space and take all appropriate actions to prevent the ingress of substances. Further information of these substances could be obtained from Site-Specific Risk Information (SSRI), site working plans or the responsible person.
Confined spaces should be securely isolated from the ingress of substances that could pose a risk to those working within the space.
An effective method used in industry is to disconnect the confined space completely from every potential source. Methods include removing sections of pipe or duct, inserting blanks or 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.
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 machinery from another, are sometimes present at a confined space and offer some degree of its isolation. 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.
Isolation of liquids may be possible in industrial-type confined spaces, such as vats and silos. However, in confined spaces affected by weather, water distribution or sewerage, it may not always be possible, so personnel should be extra vigilant and take extra precautions.
It may be possible to use appropriate submersible or other pumping equipment to remove liquids or reduce levels, or to insert inflatable bladders. However, using methods such as this should be carried out with caution as they can suddenly fail, releasing the contents.
Possible diversion of the liquid can occur which could affect other areas. The level of liquid in the confined space and the liquid being removed or sealed off should be continually monitored while personnel are inside the confined space.
Isolating the flow of a particular material into the space can be achieved in industrial-type confined spaces, such as vats and silos, with the option of shutting down the flow of materials into the space. In other situations, this may not be possible, but personnel may be able to remove the product from the space in question and eliminate the actual hazard.
Incident commanders should be aware that risks associated with free-flowing materials can include crusting of the upper surface, bridging of material and machinery, for example, a screw conveyor.
Whatever means of isolation is used, it must be tested to ensure it is sufficiently reliable by checking for substances to see if isolation has been effective.
Isolation from electrical or mechanical equipment
Some confined spaces contain electrical or mechanical equipment, with power supplied from outside the space. It may be necessary to request specialist advice or assistance for isolating hazards in confined spaces.
Power should be disconnected, separated from the equipment, and a check made to ensure isolation has been effective. However, it may be necessary to carry out a risk assessment that allows the power to remain on if necessary, for example:
- To assist with the task being undertaken
- To support vital services, such as:
- Lighting
- Communications
- Firefighting
- Ventilation
- Pumping if there is a risk of flooding
- If cables are distributing power to other essential areas or processes
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 as each operator has their own lock and key providing self-assurance of the inactivated mechanism or system. There should be a check made to ensure there is no stored energy of any kind left in the system that could activate the equipment inadvertently. For further information refer:
- Industry:Â On-site machinery
- Industry:Â Electricity