Confined spaces can be found in almost any workplace and, despite the name, are not necessarily small. Some examples include silos, vats, hoppers, utility vaults, tanks, sewers, pipes, access shafts, truck or rail tank cars, aircraft wings, boilers, manholes, ditches, trenches, and storage bins. To qualify as a confined space, the following characteristics must be present:
1. Limited openings for entry and exit: Confined space openings are limited primarily by size or location. Small openings make it difficult to get potentially life-saving protective and/or rescue equipment in when needed.
2. Unfavorable natural ventilation: Because air may not move in and out of confined spaces freely, the atmosphere can be very different than the atmosphere outside of the space. Common ventilation issues to be aware of are:
- Oxygen-Deficient Atmospheres: An oxygen-deficient atmosphere has less than 19.5% available oxygen and therefore should not be entered without an approved self-contained breathing apparatus. The oxygen level in a confined space can decrease because of work being done, such as welding, cutting or brazing; or it can be decreased by chemical reactions (rusting) or through bacterial action (fermentation). The oxygen level can also decrease if oxygen is displaced by another gas, such as carbon dioxide or nitrogen. Workers exposed to the total displacement of oxygen by another gas, such as carbon dioxide, will lose consciousness and then die.
- Flammable Atmospheres: Two things can make an atmosphere flammable: the oxygen in the air OR a flammable gas, vapor or dust in the proper mixture. An oxygen-enriched atmosphere (above 21%) will cause flammable materials, such as clothing and hair, to burn violently when ignited. Therefore, never use pure oxygen to ventilate a confined space. Ventilate with normal air. Different gases have different flammable ranges. If a source of ignition is introduced into a space containing a flammable atmosphere, an explosion will result.
- Toxic Atmospheres: Most substances (liquids, vapors, gases, mists, solid materials and dusts) should be considered hazardous in a confined space. Toxic substances can come from the product stored in the space, the work being performed in the space, and/or the area adjacent to the space.
3. Not designed for continuous worker occupancy: Most confined spaces are not designed for workers to enter and work in on a routine basis, making inspection, maintenance, repair, cleanup and other tasks difficult and dangerous due to chemical or physical hazards.