Ventilation in confined spaces

22 July 2019


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Working in confined spaces (partially or fully enclosed spaces) presents specific risks of suffocation, poisoning, fire and explosion. Most accidents, caused by an oxygen-deficient atmosphere or the presence of toxic gases or fumes, are often serious or even fatal. This is why ventilation in those spaces is essential and must be studied very seriously.

Working dangers in confined spaces

Three sewer workers, Tony, Michel and Hubert, aged 22 to 44, died in France around 10 years ago, intoxicated by the fumes of a deadly gas in a settling tank. They were working for a road company, in fact as part of a routine operation: removing sand from a tank to facilitate the flow of wastewater.
Seven years ago, a farmer died from toxic fume poisoning while trying to repair a submersible pump in a well. 

In both cases, death was caused by the inhalation of hydrogen sulphide (H2S), one of the most toxic gases that exists and yet derived from natural sources: the decomposition and anaerobic fermentation of organic substances under the oxidative action of bacteria or fungi.
This gas can be released suddenly and unexpectedly like the piercing of a hidden pouch, causing sudden death, but can also harm human health through regular breathing in small quantities. Questions are being asked here about the significant decrease in life expectancy in some industries such as that of sewer workers.

An important vigilance for operators in confined spaces

Special attention is therefore required regarding employees in local technical departments who enter sewers, workers in professional cleaning companies, maintenance technicians in water treatment plants, surveyors during crude oil inspections, laboratory experts and employees in the chemical sector etc.

Dangerous vapors

H2S gas is one of the most dangerous examples of toxic fumes that can occur in confined spaces. But there are others.It can therefore be useful to know what is considered at the professional level as a confined space, thus presenting risks for human beings. It is a fully or partially enclosed space that is neither designed nor built as a workstation and is not intended to be, but which may occasionally be temporarily occupied by persons for inspection, maintenance or repairs. Access is restricted, preventing the free circulation of air. The atmosphere in these spaces can jeopardise the health and safety of anyone entering them, due to insufficient natural or mechanical ventilation, the materials or substances they contain, and their design and location, the equipment used or the nature of the work performed there.

In confined spaces, air is low in oxygen

Breathing air contains about 21% oxygen, and with a content of about 17%, it becomes harder to breathe. Between 13 and 10%, major risks develop. It is therefore the decrease in oxygen level where the problem lies and it is much more likely in a confined space, during excessive consumption due to combustion, oxidation and the decomposition of organic matter among other things. It may also be due to the addition of inert gas such as nitrogen or natural gas release such as the fermentation of organic substrates in cereal storage, winemaking tanks and sewers etc.

Ventilate confined spaces

It is therefore clear how vital protection, detection, ventilation and extraction equipment is in these areas. Ventilation in particular improves safety because it dilutes toxic gases or fumes and provides oxygen throughout the operator’s work. Extraction is essential when there are pollutants, volatile organic compounds, or H2S.

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