WORKPLACE TOXIC GAS DETECTORS – MAJOR REVISION OF STANDARDS
Toxic gas detectors1 perform a valuable role in the
workplace by helping to reduce the risk of ill-health and death which can arise from exposure to toxic gases and vapours. An important consideration in their use is the availability of gas detector standards. These help to reassure and guide the user by setting a minimum standard so that practitioners can choose a suitable and reliable detector that is fi t for purpose, and use it effectively throughout its working life. A series of European standards for gas detectors (EN 45544 Parts 1-4) were originally published over 15 years ago to address this need. They have now recently been comprehensively revised:
procedures for the measurement of chemical agents’. General gas detection includes the following measurement tasks:
• providing visual and audible alarms to warn workers of potentially harmful toxic gas concentrations;
• providing alarm output signals to initiate operation of ventilation, shutdown of processes, safe evacuation, etc;
• area monitoring to provide continuous information on the concentration of toxic gas over a site;
• measurements to monitor the effectiveness of protection systems, e.g. extraction;
• spot-reading measurements, e.g. to obtain a gas-free work permit;
Confi ned space work
• EN 45544-1 Workplace atmospheres. Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours.
o Part 1: General requirements and test methods. (to evaluate the performance of personal, portable, transportable and fi xed detectors)
Part 2: Performance requirements for apparatus used for exposure measurement.
Part 3: Performance requirements for apparatus used for general gas detection
Part 4: Guide for selection, installation, use and maintenance
This article describes particularly how these updated standards clarify and revise the relation between the measurement tasks and their associated performance requirements (Parts 1-3), and how the “user guide” (Part 4) has been updated in the light of new knowledge.
Toxic gas detectors can reduce risk in various ways depending on the type of detector and how it is used. However, two basic measurement tasks can be identifi ed and they form the framework of the new standards:
• general gas detection, e.g. safety warning, leak detection, which is the most prevalent use of toxic gas detectors; and
• exposure measurement, as part of a workplace exposure assessment, for example, according to EN 482 - ‘Workplace exposure. General requirements for the performance of
• leak detection in industrial and commercial environments.
A particular environment where toxic gas detectors (together with oxygen defi ciency and fl ammable gas detectors) play a vital role is in confi ned spaces2
. Testing and monitoring the atmosphere
should be considered when designing a safe system of work for a confi ned space, which may form the basis of a permit to work; the atmosphere may need to be tested for the presence of hazardous gas or defi ciency of oxygen; and regular monitoring may be necessary, typically using portable (including personal) gas detectors which provide alarms.
Procedures for workplace exposure measurements, are an important part of the process of exposure assessment, which itself is required to be carried out under national laws and regulations3
.
General requirements for such procedures are specifi ed in European standard EN 482. These include unambiguity, selectivity, averaging time and expanded uncertainty4
, a correct decision can be made, for for minimum specifi ed
measuring ranges. The procedures used for such measurements should give reliable and valid results, so that when compared with occupational exposure limits5
instance, as to whether the exposure level is acceptable or control measures (e.g. containment, ventilation, respiratory protection) need to be applied. Specifi c requirements relating to the use of various types of measuring procedures and measuring devices for all types of chemical agent including direct-reading instruments for gases (EN 45544), the subject of this article, are referenced in EN 482.
EN 482 identifi es three types of exposure measurement: • Screening measurements of time-weighted average
concentration performed to obtain semi-quantitative information on exposure levels to identify potential health hazards, estimate the health risk and determine if the exposure is signifi cantly below or above the occupational exposure limit.
• Screening measurements of variation of concentration in time and/or space - performed to provide information on the likely pattern of the concentration of chemical agents in the air; identify locations and periods of elevated exposure; provide information on the location and intensity of emission sources; and estimate the effectiveness of control measures, e.g. ventilation.
• Measurements for comparison with occupational exposure limits and periodic measurements - comparison measurements are performed to obtain results of known uncertainty for the average concentration of a chemical agent in the air in a worker’s breathing zone. Periodic measurements are performed to determine whether exposure conditions have changed or whether control measures remain effective.
The requirements for exposure screening measurements are usually less stringent than those for exposure measurements used for comparison with limit values and periodic measurements because the latter two types have regulatory implications.
Performance requirements (Parts 1-3)
The performance requirements for gas detectors depend on the purpose for which they are used. This is refl ected in the latest versions of the toxic gas detector standards which have revised and clarifi ed the distinction between the requirements for general gas detection (by far the most common use of gas detectors) and exposure measurement (a more specialised and demanding use, requiring calculation of uncertainty budgets).
It should be noted that the same detector may be used for general gas detection applications (EN 45544-3) and exposure measurements (EN 45544-2). Moreover, a detector used for general gas detection could be certifi ed under the tougher requirements of EN 45544-2, for example, to possibly confer on the manufacturer a market advantage for accuracy.
Detectors for general gas detection are subject to performance requirements for the various tests comparable with those for fl ammable gas detectors (c.f. EN 60779-29-1), i.e. the deviation from the reference value must be less than a certain value for
IET Annual Buyers’ Guide 2016/17
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