Long term protection
October 1st 2004

Never mind making it home for your tea, what about enjoying your retirement? By Paul Walton Most people understand the need to protect workers in confined spaces from the direct threat of gases. But now there is realisation of the need to monitor for longterm problems. The HSE define in their publication EH40 the maximum concentrations to which an unprotected worker may be exposed. Above these concentrations, the air is deemed to be hazardous. Unprotected workers should not be allowed to remain in those conditions for any reason. A confined space may be a sewer, tunnel, duct, vessel or even a trench. Typically a multigas monitor is used to warn of dangerous levels of Oxygen and explosive gases, plus toxic gases such as Carbon Monoxide and Hydrogen Sulphide. Indeed the standard four-gas confined space monitor has just this configuration. But there may also be Volatile Organic Compounds (VOCs) present and these can pose just as big a risk, if not as imminently. Some VOCs are dangerous to health even at very low concentrations.

Why do we monitor gases?

There are three basic reasons why we monitor gases - Safety, Health and Comfort. By comfort we mean that if for example there is overcrowding in an area, there may be a rise in the levels of Carbon Dioxide. Even at levels which do not threaten health or safety, people may feel uncomfortable. If there is an immediate threat of death or injury we need to warn workers of an unsafe condition, so they can evacuate the area or take avoiding action. However their health may still be at risk even if there is no immediate problem. VOCs can be carcinogenic for example. While a four-gas confined space monitor may ensure you get home safe for tea, it may not ensure you live to enjoy retirement! Many industrial organisations are users of VOC’s.

They may be found in hospitals, universities and colleges as well as chemical and petroleum plants.

Hazards arise from print solvents, solvents in adhesives and degreasing agents, in addition to fugitive emissions from hydrocarbons.

The solution is to monitor for low levels of Volatile Organic Vapours in addition to the four standard gases.

This can be easily achieved using a PhotoIonisation Detector (PID). Modern PIDs are lightweight and easily carried when working. A Photoionisation Detector uses an ultraviolet light to break down the compound into positive and negative ions that can easily be measured with a detector. This detector measures the charge of the ionised gas and converts the signal into current.

The current is amplified and displayed on the meter as a parts-per-million reading of the compound.

Datalogging

Datalogging is a highly useful feature of modern instruments. While the monitor provides an immediate warning to the worker of high levels, datalogging will also allow the manager to identify a profile of the workers exposure. With capacity for frequent logging over an eight-hour period, data is easily sent to a PC in report and graphical format. The graphical format will allow managers to pinpoint high concentrations.

Through consultation with the worker, it should be possible to identify why these peaks occurred, and action may then be taken to avoid these high exposure periods in future. For example, the worker could have turned off the ventilation for a short period. The data record would immediately highlight an increased level of exposure. Individual workers may be unwittingly exposing themselves to high levels without realising the dangers. A graphical record showing a severe, high spike would give rise to suspicion of unacceptable working practices. By carrying out routine monitoring of workers and archiving their exposure details, you have documentary evidence that the workers exposure has not exceeded the requirements of EH40. Some simple four-gas monitors now have “wrap-around” datalogging.

This means that even if records are not routinely kept, a constant datalogging record is retained in the memory, so if an incident occurs there is always evidence in the instrument of what happened and when.

Small and Lightweight

Four-gas monitors are now small and lightweight which enables them to be clipped to a belt or harness.

PIDs come in all shapes and sizes. Most will clip to a belt or harness and some will even fit in a breast pocket. And the latest compact four-gas monitors come with a VOC detector built-in, making it really simple to ensure workers are protected from the long term risks as well as the imminent ones. So if you not only want to get home for tea, but also want to enjoy retirement, use a PID as well as the standard four-gas confined space monitor.

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