Confined environments: the danger of asphyxiation

17 June 2022

An important number of serious accidents at work occur in confined environments where dangerous atmospheres are present or accidentally formed: asphyxiating, toxic, flammable or explosive.

It is unacceptable given the progressive trend of current legislation and actions aimed at training by accredited bodies / operators.


Asphyxiating substances: terms and definition

The concentration of oxygen present in an unaltered air sample is approximately 20,9 % of the total oxygen volume/volume (v/v). When this percentage reaches down to 19.5 v / v the air is considered deficient in oxygen while when the concentration drops further to below 16 5 you get into a very dangerous situation for humans.

Oxygen reductions occur for:

  • fire
  • chemical reaction
  • replacement of oxygen with other gases.

In reverse, the degree of flammability of gases and materials increases. In fact, if the oxygen level is enriched and exceeds 24%, items such as clothing can undergo spontaneous combustion.

As for asphyxiating substances here you will find an example list:

  • Halogen acids
  • sulfur dioxide
  • phosphorus
  • pentacloruri
  • carbon dioxide


Risks associated with asphyxiating substances

The presence of asphyxiating substances in confined environments would lead to a very high risk for the operator.

To recognize spaces confines suspicions of pollution even before the assessment, which is always mandatory, we report some cases:

  • places where there is a reaction between oxygen and waste;
  • places where there is an increase in carbon dioxide that replaces the air where there is soil water and limestone and that a reaction is triggered between these;
  • in the holds of ships, in containers, in tankers in which the substances contained react with the oxygen present inside;
  • in steel tanks where oxidation produces rust;
  • in non-aerated places where extinguishing agents such as carbon dioxide or halogenated agents are used on the surface;
  • places where bulk solids or granules once merged can suddenly collapse suffocating overwhelmed people
  • environments and containers in wineries

Remember that it is always necessary to check that the air is free from asphyxiating, toxic and flammable chemical agents and that it is suitable for breathing.


Reference legislation

The regulatory reference is mainly constituted by Legislative Decree 81/08, in particular Title II describes the most specific aspects for workplaces suspected of pollution. First of all, art. Article 66 establishes the prohibition of access to environments suspected of pollution before having ascertained the absence of danger. The same article also provides some indications regarding the safety measures to be adopted in case of doubt about the quality of the atmosphere, greater indications are expressed in Annex IV to copy 3 “tanks, ducts, pipes, tanks, containers, silos.



It could happen that, despite the risk assessment of a confined environment done correctly and dpi in excellent condition, the operator may suffer a case of asphyxiation.

We remind you that it is essential to work according to the specific training for environments in confined spaces and the directives received and carried out in the documents used for use as information material for all the figures involved.

The symptoms of asphyxiation are distinguishable first of all from the difficulty of breathing of the affected person that is not always accompanied by loss of consciousness. When there is a mechanical respiratory obstruction, the color of the skin and especially of the lips changes to purplish. If the cause should be for carbon monoxide then as an obvious symptom will be the change of the skin in cherry red color. When, on the other hand, the operator will be unconscious and in respiratory arrest if the complexion of the skin will be white bruised most likely he has come into cardiac arrest.

The importance of courses for confined environments

It is a particular area in which the competence is necessary to know how to move and there are situations in which the perception of danger is not immediate.

The course implements the provisions of Presidential Decree 177/11 which identifies the criteria for the qualification of companies and self-employed workers operating in environments suspected of pollution or confined, pursuant to Article 6, paragraph 8, letter g), of Legislative Decree 81/08 and subsequent.m amendments.

Valeria Leone,2013 ,Asissia ,come intervenire?, Humanitasalute .


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