Oxygen Deficiency in confined spaces: Is it Safe to Enter?

Injury or death due to oxygen deficiency is a common hazard in many industries. Toxic gas is often to blame when workers die unnecessarily due to asphyxiation in environments where the oxygen is actually depleted by gases such as nitrogen. To prevent these accidents, government and other agencies have implemented numerous regulations, required procedures, permit processes, as well as enforcement actions.

Breathing air contains 21% Oxygen. If the Oxygen decreases by as little as 1.5%, the human body will be affected.
Reduced Oxygen is also believed to have long-term detrimental affects on the human body.


Oxygen Content of Air Signs and Symptoms
15%-19.5% Decreased ability to work strenuously. May impair co-ordination and may induce symptoms in persons with coronary, pulmonary, or circulatory problems.
12%-15% Respiration deeper, increased pulse rate and impaired co-ordination, perception and judgement.
10%-12% Further increase in rate and depth of respiration, further increase in pulse rate, performance failure, giddiness, poor judgement and blue lips.
8%-10% Mental failure, nausea, vomiting, fainting, unconsciousness, ashen face, blue lips.
6%-8% 8 minutes may be fatal in 50-100% of exposures; 6 minutes may be fatal in 25-50% of exposures; 4-5 minutes, recovery with treatment.
4%-6% Coma in 40 seconds, convulsions, respiration ceases, death.

These values are approximate and may vary depending on an individual’s health, physical activity and the specific working environment that they encounter.

Examples of confined spaces include:

  • Ballast tanks
  • Boilers
  • Cargo compressor rooms
  • Cargo holds
  • Cargo pumprooms
  • Cargo tanks
  • Chain lockers
  • CO2 Rooms
  • Cofferdams
  • Dry bulk tanks
  • Duct keels
  • Engine crankcases
  • Engine scavenge air receivers
  • Foam tanks
  • Fuel tanks
  • Inter barrier spaces
  • Oil spill dispersant tanks
  • Potable water tanks
  • Sewage tanks
  • Stool spaces
  • Void spaces
  • Waste oil tanks

Sigma has both fixed installation monitors and hand held units. Contact us for details