application note


Working safely in confined spaces


What is a confined space?


Confined spaces pose various hazards for operators and can be found in a wide variety of industries and applications. A confined space can be defined by a number of factors; the space itself must be large enough for a worker to enter but is not suitable for continuous worker occupancy. A confined space is also defined as having limited openings for entry and exit. Examples of confined spaces found in industry include aircraft fuel tanks, underground utility vaults and wine fermentation tanks.


Due to their small size, gas hazards can quickly build up in confined space environments. Some confined spaces may require permits to enter, owing to the fact that they contain potentially hazardous atmospheres or materials that have the potential for engulfment. Inwardly sloping walls or floors can also pose dangers, because they reduce the volume of the space, and may also require a permit to enter.


Regardless of whether the area is permit required or not, all confined spaces should be treated as potential hazards.


Likely hazards encountered in confined spaces


Typically, confined spaces can contain a variety of hazards including Hydrogen Sulphide (H2


S), Carbon Monoxide (CO), Methane (CH4


• H2 H2


S S is a toxic gas that is produced as a bi-product


of microbial activity. This gas is highly toxic and at concentrations less than 30ppm is identifiable by its strong odour of rotten eggs. At concentrations higher than 30ppm, H2


S paralyses the olfactory nerve, stopping the sense of smell. At concentrations of 500 to 700 ppm, death will occur within 30 mins to 1 hour. For further information on the dangers of H2


feature on page 10. • CO


CO is a toxic gas that is produced by the incomplete burning of fossil fuels such as oil, gas and coal. During normal combustion, Carbon Dioxide is produced (CO2


) but when


ventilation is inadequate, CO can be produced instead. CO is absorbed by haemoglobin in the blood and prevents Oxygen being absorbed, causing the victim to die of asphyxiation. At concentrations of 400ppm, CO will start to cause nausea, dizziness, headache and sickness. At concentrations of 800ppm, death will occur half an hour after exposure.


Page 18 | GasDetector | Winter 2011 S please click here to read our extended ) and Oxygen deficiency.


• CH4 CH4


is a combustible gas that is produced by the decomposition of organic materials. CH4


is the main


constituent of Natural Gas and as a result, leaks in gas pipes can be another source of Methane.


• Oxygen Deficiency Normally Oxygen makes up 21% of the atmosphere and an Oxygen deficient environment is described as being one where Oxygen levels are 19.5% or less. Oxygen can be displaced by toxic or inert gases and microbial action. Oxidation caused by rusting metal and combustion can also cause an Oxygen deficient environment. At 19.5% Oxygen the operator will feel drowsy. At 17% and less cognitive processes and coordination will be severely compromised. At levels of 6% or lower, death will occur quickly.


Although these are the most likely gases to be encountered in confined spaces, other gases can also be found.


Click here for more information on CO safety at home. Call: +41 (0) 44 943 4300 or visit: www.honeywellanalytics.com


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