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9.2 Confined Spaces in Construction
A confined space has limited openings for entry and exit, poor natural ventilation that could trap or produce dangerous air contaminants, and is not meant for continuous occupancy. They are found in steel mills, paper mills, shipyards, farms, public utilities and construction. Examples include storage tanks, ship compartments, process vessels, pits, silos, vats, wells, sewers, digesters, degreasers, reaction vessels, boilers, ventilation and exhaust ducts, tunnels, underground utility vaults and pipelines.
Classification and configuration
Confined spaces fall into two groups:
- Open topped enclosures with depths that restrict natural air movement, such as degreasers, pits and some tanks and excavations.
- Enclosures with limited openings, such as sewers, tanks and silos.
The hazards are decided by the material stored or used, the process taking place and the effect of the outside environment. An open space has no obstructions, such as a water tank. An obstructed space has something, such as a baffle or mixing blade, that a rescuer would have to work round. Work in such spaces happens during construction, inspection, repair and maintenance.
Key terms
| Term | Meaning |
|---|---|
| Permit space | A confined space that has a hazardous atmosphere, a material that could engulf an entrant, a shape that could trap, or any other serious hazard. |
| Non-permit space | One with no hazard capable of causing death or serious harm. |
| Acceptable entry conditions | Conditions that must exist for entrants to enter and work safely. |
| Entry permit | The written document that allows and controls entry. |
| Attendant | A person outside who monitors the entrants and carries out the program's duties. |
| Authorised entrant | A worker the employer authorises to enter. |
| Entry supervisor | The person responsible for the entry operation. |
| Hot work permit | Written authorisation for work that can provide a source of ignition, such as riveting, welding, cutting, burning and heating. |
| Inerting | Displacing the atmosphere with a non-combustible gas, such as nitrogen. |
| Oxygen deficient | Less than 19.5 percent oxygen. |
| Oxygen enriched | More than 23.5 percent oxygen. |
| Retrieval system | A line, harness and lifting device or anchor for non-entry rescue. |
| Testing | Identifying and evaluating the hazards for entrants, including the tests to be done. |
The written program
Entering and working in a confined space can expose a worker to an oxygen deficient or toxic atmosphere and to the release of hazardous energy: electrical, mechanical, hydraulic and chemical. The employer needs a comprehensive written confined space program that:
- identifies all confined spaces
- posts a warning sign at the entrance to each
- evaluates the hazards of each type
- includes a job safety analysis for each task
All workers who must enter must be told about the hazards, the precautions to take and how to use the protective and emergency equipment.
Duties
Attendants know the hazards and the signs of exposure, are aware of possible behavioural effects on entrants, keep an accurate count of entrants, stay outside until relieved by another attendant, communicate with entrants, and monitor activities inside and outside the space.
Entry supervisors know the hazards; check that all tests and procedures on the permit have been done and the equipment is in place before signing the permit; check that rescue services are available and can be called; remove unauthorised people who try to enter; and decide when responsibility for the entry is passed on.
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