Dealing with Confined Space Entry


Confined spaces can be found in a wide variety of industries and applications and these environments can present an array of hazards for operators. As the name might suggest, a confined space is a location with a limited volume size and can be defined as having the following attributes:


• The space itself must be large enough for a worker to enter but be too small to allow continuous worker occupancy to take place


• The area features limited openings for entry and exit, causing air flow to be compromised


There are many examples of confined space environments in


industry including aircraft fuel tanks, underground utility vaults, wine fermentation tanks and sewers.


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 sources of potential gas hazards.


Why are confined spaces dangerous?


The limited volume size in a confined space allows dangerous gases to build up more quickly. In addition, inadequate air flow can allow the displacement of Oxygen by other gases, causing the risk of asphyxiation to an operator entering the area.


Some confined spaces require a permit to enter, due to the danger associated with them. Regardless of whether a permit is required, all confined spaces should be treated with caution and these environments need to be fully evaluated for hazards before they are entered. This includes stratified testing of the atmosphere in the space, prior to entry, to ensure it is free of gas hazards.


haemoglobin in our 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. CO has no odour, it is invisible and highly toxic.


CH4


CH4 or Methane is a combustible gas that is produced by the decomposition of organic materials. CH4 is also the main constituent of Natural Gas (typically makes up 94% – 98% of natural gas) and as a result, leaks in gas pipes can be another source of Methane.


Oxygen Deficiency Normally Oxygen makes up 20.9% of the atmosphere and an Oxygen deficient environment is described as one where Oxygen levels are 19.5% or less. Oxygen can be displaced by toxic or inert gases. 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. Some confined spaces – such as ships – are filled with an inert


gas to limit the amount of O2 below 2% and thus the risk of an explosive atmosphere.


Although these are the most likely gases to be encountered in confined spaces, other gases can also be found. This means that the use of a multi-gas portable is essential for any worker planning to enter this type of location.


Conducting a pre-entry check before entering a confined space


Testing the atmosphere of a confined space at all levels is essential as some gases are heavier


than air (such as H2S, which is slightly denser than air), some lighter (such as CH4), and some the same density (such as CO). It’s


important to use a multi-gas detector capable of monitoring for the gas hazards expected to be in the location in question.


A multi-gas portable capable of providing


What gas hazards are likely to be encountered in confined spaces?


Typically, confined spaces can contain a variety of hazards including


Hydrogen Sulphide (H2S), Carbon Monoxide (CO), Methane (CH4) and Oxygen deficiency.


H2S H2S or Hydrogen Sulphide is a toxic gas that is produced as a by-product of microbial activity. It is highly toxic and at concentrations less than 30ppm is identifiable by its strong odour of rotten eggs. At concentrations


higher than 30ppm, H2S 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. Hence you cannot rely on smell: you need a gas detector.


CO


CO or carbon Monoxide 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 there is not enough Oxygen, CO can be produced instead. CO is absorbed by


simultaneous monitoring of H2S, CO, Oxygen and combustibles (%LEL) is essential for safe confined space entry (please note: the sensors used with any portable device must reflect the known hazards likely to be in the environment). Additional protection can be provided by a 5-gas portable gas detector, allowing an extra sensor to protect against other


potentially deadly gas hazards that are specific to a jobsite or industry.


To avoid unnecessary risk, the operator should not directly enter the area but test the atmosphere from outside of the confined space. The use of a gas monitor and pump combined with a sampling hose will allow the operator to take readings at various levels, without actually having to enter the area themselves. Sampling hoses are available at different lengths to fit the different confined space requirements.


Many gas detection companies like BW


Technologies by Honeywell can provide confined space gas detector kits, which include all the equipment needed to safely monitor a confined space prior to entry. Some devices, like the GasAlertMax XTII and the GasAlertMicro5 from BW Technologies by Honeywell are already optimised for confined space use with an integrated pump and a sampling hose with particulate filter supplied as standard.


Once the space has been fully evaluated for


gas hazards and is deemed to be safe for worker occupancy, it’s important to keep continuously


November/December 2010


IET


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