Safety Matters, While Working in Confined Spaces Part 1

This article has been written out of personal and institutional experiences and should not be taken as a formal guideline for working in confined spaces. Please refer to relevant safety manuals before undertaking such work.

Definition of Confined Space – A space that has any one or multiple characteristics indicated below is deemed to be “Confined Space”:

  •  Limited number and / or size for entry and exit for the space. Examples – Water tanks / Fuel or oil storage silos / Manhole chambers in sewerage lines etc. Man hole sizes may be very small restricting fast movement. There may be just one manhole provided in a tank.
  • Unfavourable natural ventilation. Example – Water and oil tanks are normally kept hermetically sealed to avoid contamination from outside, hence there is no natural ventilation. Manholes in sewerage lines may have some ventilation due to its widely connected network but may not be able to sustain life. Toxic or inflammable gases may occupy the spaces.

  • Not designed for worker occupancy normally. ExampleThis could be material storage rooms in basement areas, with very low or no ventilation due to various reasons. May not have life-sustaining gases, but may have other non-life sustaining or toxic gas concentrations.

Some of the confined spaces found in workplaces may have a combination of all the above characteristics, complicating the working within the spaces and emergency rescue operations. Hazards identification needs to be thorough and foolproof in all the above cases.

Hazardous Atmospheres

The atmosphere within a confined space could become hazardous because of lack of natural air movement. This could lead to the atmosphere being:

  •  Oxygen deficient (Less than 19.5%). An existing atmosphere within a confined space may be Oxygen deficient. Further Oxygen depletion could occur due to human physical activity within, welding, cutting, chemical reaction (rust formation, fermentation etc). Oxygen could get displaced by heavier non life-sustaining gases such as Carbon dioxide or Freon or Hydrogen Sulphide. If the Oxygen level is less than 19.5%, entry is to be restricted and allowed wearing Self Contained Breathing Apparatus (SCBA) only.
  • Toxic. Toxic atmosphere could be found in confined spaces due to:

    • Gases coming out of the residue left in the tank even after the bulk of the material has been evacuated. This could be sticking to the side walls or settled to the bottom of a tank. Dangerous Hydrogen Sulphide gas can emanate out of decomposed material.

    • Even fresh water tanks could have hazardous gases such as Chlorine which is not life-sustaining.

    • Bi-products of work such as cutting / brazing / painting / cleaning /  can form a hazardous mixture of gases within confined spaces.

    • Gases from an adjacent compartment or work space could enter a confined space and remain trapped there.

    • Material handled could form concentrated toxic gas areas, even with partial ventilation. Sewerage inspection chambers could trap lethal gases from the sewer.

  • Flammable. When three essential components, namely, (a) presence of Oxygen, (b) a flammable mixture of vapour / gases / dust and (c) a source of ignition are present together in a space, fire and explosion are inevitable. Different gases / vapour / dust have different levels flammability. A small electric spark from a motor or even a breaker contact could form the source of ignition. An oxygen enriched atmosphere (with more than 21% Oxygen) can cause inflammable material to auto-ignite and burn violently.

To be continued in Part 2 of this series. Part 2 contains thoughts on “Testing the atmosphere within confined spaces”, “Isolating the confined spaces”, “Other likely hazards within confined spaces”, “Personal protection gear”, “Support team” and “Training” aspects.

Advertisements