1) Having limited or restricted means of entry or exit 2) Is large enough for an employee to enter and perform assigned work 3) Is not designed for continuous occupancy
Examples include underground vaults, silos, storage bins, pits, tanks, sewers, and so forth.
A subset of confined spaces are permit required confined spaces which are particularly hazardous due to the presence of one or more of the following:
1) Contains or has the potential to contain a hazardous atmosphere 2) Contains a material that has the potential for engulfing the entrant 3) Has an internal configuration that might cause an entrant to be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross section 4) Contains any other recognized serious safety or health hazards.
Such situations are particularly dangerous for a potential rescuer, as there is an immediate desire to effect a rescue. Unfortunately, due to the presence of conditions that may be immediately hazardous to the safety of the would-be rescuer, until confined space rescue standards were developed and followed, many rescuers have died attempting to save others. One study conducted revealed that 1.6 rescuers died for every initial victim- a surprising statistic that revealed a greater problem in which fire departments and other responsible parties simply sent in more people, who also died without being retrieved successfully.
In the USA, confined space rescue is covered under National Fire Protection Agency (NFPA) 1670, and under 29 CFR 1910.146 and 29 CFR 1910.147.