Safety in confined spaces
October 1st 2006 Aconfined space is defined in the Health & Safety Commission's approved code of practice L101:1997. Employers are required to evaluate the risks such workplaces pose to their employees and monitor to prevent them. In most cases, the assessment and the safe working system will require testing of the atmosphere with gas detection equipment. There are three main gas risk categories: combustible, toxic, and high or low oxygen levels. David Riddle, Crowcon Detection Instruments' Portables business development manager, discusses the risks and suggests solutions Combustible gas risks: For combustion to occur, the air must contain a minimum concentration of combustible gas or vapour at the so-called lower explosive limit (LEL). At concentrations equal to or greater than this, combustion will occur in the presence of an ignition source. For most combustible gases and vapours, the LEL is less than 5% by volume, and a combustible atmosphere is usually described as 'hazardous' at 10% LEL or higher. Storage vessels which have contained hydrocarbon fuels and oils present an obvious danger. Other dangers come from fuel leaks: pipelines, gas cylinders and engine-driven plant. For workers in pits and sewers, methane from decaying organic matter is an almost universal danger. Toxic gases and vapours: Confined space workers may be exposed to a large number of toxic compounds depending on the nature of the work. A risk assessment should therefore be made of which toxic substances a worker may be exposed to in any given work situation. When generators, for example, are used in a confined space, carbon monoxide and oxides of nitrogen in the exhaust fumes create a serious poisoning risk. Hydrogen sulphide is a persistent hazard in the waste water and oil industries. Oxygen - too high or too low? The normal concentration of oxygen in fresh air is 20.9%. An atmosphere is hazardous if the concentration of oxygen drops below 19.5%. If the concentration falls below 17%, mental and physical agility are noticeably impaired and death comes very quickly if it drops significantly further. At very low levels unconsciousness takes hold so rapidly that the victim is unaware it is even happening. Equipment types: Both portable and fixed instruments can be used for confined space monitoring. Fixed systems typically have one or more detector heads connected to a separate control panel; if a dangerous gas level is detected, the panel raises the alarm by triggering external sirens and beacons. This sort of installation is suited to locations like plant rooms, which have sufficient room for the hardware. Crowcon, for example offers fixed devices such as the Xgard gas detector, which is available with a wide range of specific gas sensors, and the Nimbus infrared flammable gas detector. Control panels such as Vortex and Gasmaster provide simple monitoring and alarm functionality. Much confined space work takes place, by definition, in areas not normally occupied, making pre-entry testing checks mandatory. These checks are carried out using compact, portable units which may then be used for continuous monitoring by personnel entering the confined space. By combining one or more sensors with powerful audible and visual signals, portable detectors can be carried or worn wherever they are needed. Single hazard: The simplest portable detectors contain a single sensor for a specific gas and are suitable for protecting workers where a risk assessment has identified only one foreseeable hazard. These products, such as Crowcon's Eikon personal gas alarm, are disposable. Activated by the user when first required, they run continuously without maintenance for a set period, typically two years, and are suitable where there is no training facility. Full function, non-disposable, single gas detectors have rechargeable or replaceable batteries and an illuminated display showing gas levels and other information. They usually also offer datalogging of recorded gas levels. The Gasman from Crowcon, for example, is available in versions for flammable gas, oxygen or toxic gas in the same package. Multi-hazard: If more than one hazard is likely to be encountered in a single area, multi-gas instruments are used. These can monitor up to four gases at once, such as combustible hydrocarbons, oxygen, hydrogen sulphide and carbon monoxide. Crowcon's Tetra and Tetra: 3 are examples. Some multi-gas detectors, like the Tetra, also have a built-in sampling pump, allowing a sample line to be fed into the space while the monitor remains outside with the user. This enables the user to test the atmosphere before entry into the confined space. Universal features: All portable gas detectors should have certain features in common. They should have impact-resistant casings and a high degree of protection against dust and water ingress. They should also be light and compact enough to wear for an entire shift. Finally, because of the difficulties of working in a cramped space, they should be easy to use. No matter how advanced a detector is, the user should be faced with nothing more daunting than a clear display and simple, one-button operation. Crowcon detectors have all these features as standard. More articles from Crowcon Detection Instruments Ltd: | 
