The most common hazards that should be recognized and associated with entry into a confined space can be categorized as follows:
A. Oxygen Deficient Or Enriched Atmospheres: Normal air contains approximately seventy eight percent (78%) nitrogen and twenty and ninety five-tenths percent (20.95%) oxygen by volume with the remaining composition made up of gases, such as argon, carbon dioxide, etc. When oxygen falls below nineteen and five-tenths percent (19.5%), asphyxiation is threatened. Likewise, when an atmosphere contains more than twenty three and five-tenths percent (23.5%) of oxygen, it can be an extremely flammable atmosphere and creates a hazard. Confined spaces with either oxygen deficient or oxygen enriched atmospheres should not be entered unless they are properly controlled, as through appropriate ventilation.
B. Flammable/Combustible Atmosphere: Two (2) situations exist which create flammable atmosphere: the availability of oxygen in the air; and a flammable gas, vapor or dust in the proper mixture. If a source of ignition is present or introduced into a confined space with the right combination of combustible gas, vapor or dust and air, an explosion will occur.
C. Toxic Atmospheres: Any chemical exhibiting toxic properties in a confined space is a cause for concern. In these cases, no entry should be made until the atmosphere is properly controlled, or the entrant is properly protected. All chemicals have a concentration at which a toxic response is elicited. Most chemical substances should be considered hazardous in a confined space because of the lack of air distribution.
D. Engulfment Hazards: Engulfment hazards exist in confined spaces by the surrounding and capture of a person by finely divided particulate matter, such as grain, sand or any liquid, resulting in suffocation.
E. Other Hazards/Physical Hazards (Noise, Heat, Cold, Etc.): This category primarily involves mechanical or crushing hazards, other than engulfment, and electrical hazards that can be safely guarded against by the proper implementation of procedures required by the City's lockout/tagout procedure, chapter 5 of this title. (2019 Compilation)