42 Gas Detection the manufacturer.
• Type HM (Health Monitoring) ‘occupational exposure’ equipment: For occupational exposure measurement, the performance requirements are focused on uncertainty of measurement of gas concentrations in the region of Occupational Exposure Limit Values (OELV).
The development of this international standard is ongoing.
In conclusion, it is anticipated that the publication of these standards at an international level will help to further improve the reliability and effectiveness of toxic gas detectors and in doing so reduce the risk of fatalities and ill-health from exposure to toxic gases in the workplace.
Bibliography BS EN 1540 (2011) Workplace exposure. Terminology. (BSI)
BS EN 45544-1 (2015) Workplace atmospheres. Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours. Part 1: General requirements and test methods (BSI)
BS EN 45544-2 (2015) Workplace atmospheres. Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours. Part 2: Performance requirements for apparatus used for exposure measurement (BSI)
BS EN 45544-3 (2015) Workplace atmospheres. Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours. Part 3: Performance requirements for apparatus used for general gas detection (BSI)
Gas testing a fixed detector
to alarm: generally, the time of response is independent of gas concentration, whereas the time to alarm decreases with increasing gas concentration for a given alarm set point. It should be noted, however, that for gases that sorb strongly on the sensor and sampling lines (e.g. hydrogen sulphide, nitrogen dioxide, VOCs) the time of response can increase significantly at low concentrations. Thin films of water or contamination on surfaces can also greatly increase the time of response, especially for water soluble gases (e.g. ammonia, chlorine).
EN 45544-2 and EN 45544-3 specify that the times of response t50
and t90 8 do not exceed 60 s and 150 s. These are general
purpose, minimum requirements covering all gases and reflect current gas sensor technology. However, for some critical applications e.g. warning of short term health effects, the response time should be as short as possible.
Following the development of this revised European standard, IEC and ISO, collaborating in similar fashion to CENELEC and CEN, initiated in 2014 a Joint Working Group (JWG) for the development of an international standard for workplace toxic gas detectors:
• IEC 62990-1 Workplace atmospheres Part 1: Gas detectors. Performance requirements of detectors for toxic gases. Also numbered as ISO IEC 20435-1.
Again, two types of detector are classified, reflecting the analogous roles of IEC and ISO to those of CENELEC and CEN respectively, but using slightly different terminology:
• Type SM (Safety Monitoring) ‘general gas detection’ equipment: For general gas detection applications (e.g. safety warning, leak detection), the performance requirements are focused on alarm signalling. The measuring range is defined by
BS EN 45544-4 (2016) Workplace atmospheres. Electrical apparatus used for the direct detection and direct concentration measurement of toxic gases and vapours. Part 4: Guide for selection, installation, use and maintenance (BSI)
BS EN 482 (2012) Workplace exposure. General requirements for the performance of procedures for the measurement of chemical agents (BSI)
BS EN 60079-29-2 (2015) Explosive atmospheres. Gas detectors. Selection, installation, use and maintenance of detectors for flammable gases and oxygen. (BSI)
BS EN 689 (1995) Workplace atmospheres. Guidance for the assessment of exposure by inhalation to chemical agents for comparison with limit values and measurement strategy (BSI)
Center for Chemical Process Safety & American Industrial Hygiene Association. (2009) Continuous monitoring for hazardous material release. (John Wiley)
EC (1998) Council Directive 98/24/EC of 7 April 1998 on the protection of the health and safety of workers from the risks related to chemical agents at work (fourteenth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC)
GESTIS Database: International limit values for chemical agents (IFA)
http://www.dguv.de/ifa/en/gestis/limit_values/index.jsp
Greenham L., ed. (2012) The CoGDEM guide to gas detection. (ILM Publications)
HSE (2013) Control of substances hazardous to health (6th edn). The Control of Substances Hazardous to Health Regulations 2002. Approved Code of Practice and guidance. L5. (HSE)
HSE (2014) Safe work in confined spaces. Confined Spaces Regulations 1997. Approved Code of Practice, Regulations and guidance. L101. (HSE)
Roe M.T.A. (2013). The importance of real-time and near real-
time detection instrumentation and methods for human exposure measurement, Ch. 2 in Important Instrumentation and methods for the detection of chemicals in the field. Smith P A and Cook G W (eds.). (AIHA)
Walsh P, Evans P, Lewis S, Old R, Greenham L, Gorce J-P, Simpson P and Tylee B. (2011) BOHS Technical Guide Series No. 15 (2nd Edition) Direct-reading devices for airborne and surface chemical contaminants. (BOHS) Online:
www.bohs.org/library/technical- publications/
Acknowledgements
I wish to acknowledge the contribution of my fellow members of the CEN/CENELEC JWG who developed this standard: J Kieswetter (DE), J Gilby (UK), G Sagasser (DE), E Wasserle (DE), K Vossen (DE), R King (UK), A Pachole (PO), I Iglesias (ES), R Bouzas (ES), G Frigo (IT), J Noeller (DE), C Sanchez (FR), B Piquette (FR). Also, thanks to Leigh Greenham (CoGDEM) for help with the content and encouragement.
This publication and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.
Notes 1
Also known as direct-reading instruments/apparatus/monitors/ equipment and continuous measuring instruments in common parlance and standards’ terminology. 2
In Great Britain, the Confined Spaces Regulations, with its associated Code of Practice, apply. Over the last 4 years in GB, there were between 1-5 deaths p.a. and 7-15 incidents in confined spaces of which 13% were due to asphyxiation and poisoning. 3
For example, European Council Directive 98/24/EC, the Chemical Agents Directive, is enacted in the UK as the Control of Substances Hazardous to Health Regulations - COSHH. 4
For definitions see BS EN 1540 ‘Workplace exposure
Terminology’ which specifies terms and definitions related to the assessment of workplace exposure to chemical and biological agents. 5
For a given measurement task, the measurement range over which the requirements for the relative expanded uncertainty have to be met depends on the limit value. However, for most chemical agents the limit values have not been harmonized, therefore a reference value (standard test gas concentration) is used instead of the limit value for the performance tests in EN 45544-1. The values chosen are equal to or close to the limit values used in European countries. 7
The occupational exposure limit value is the limit of the time- weighted average of the concentration of a chemical agent in the air within the breathing zone of a worker in relation to a specified reference period. Different countries may use different values for describing safe levels of potentially toxic substances, see for example, GESTIS (see Bibliography) which is a collection of publicly available databases on hazardous substances. 6
STEL – short term exposure limit, the averaging period typically specified as 15 min in regulations (e.g. COSHH in GB; TWA – time weighted average, the averaging period typically specified as 8 hr for long term exposure in regulations. 8
t50 and t90 are the times to reach 50% and 90% of the final indication for an increase in toxic gas concentration.
Author Contact Details Peter Walsh Health and Safety Executive • Health and Safety Laboratory, Harpur Hill, Buxton SK17 9JN, UK • Tel: 07712676624 • Email:
peter.walsh@hsl.gov.uk • Web:
www.hsl.gov.uk
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