Explosive atmospheres — Part 29-4: Gas detectors — Performance requirements of open path detectors for flammable gases

This part of IEC 60079-29 specifies performance requirements of equipment for the detection and measuring of flammable gases or vapours in ambient air by measuring the spectral absorption by the gases or vapours over extended optical paths, ranging typically from one metre to a few kilometres. 

Such equipment measures the integral concentration of the absorbing gas over the optical path in units such as LFL metre for flammable gases. 

Note 1 Actual values of concentration can be deduced only where it can be established that the concentration is uniform over the optical path, for example in very short optical paths (<100 mm). In such cases, the equipment is within the scope of IEC 60079-29-1. 

Note 2 This Standard is based upon present absorption techniques using infrared radiation. Other techniques and applications may require additional test considerations (e.g. pressure test). 

Equipment falling within the scope of this standard is classified by the following types:

Type 1: an optical transmitter and receiver, located at either end of a path through the atmosphere to be monitored. 

Type 2: an optical transceiver (i.e. combined transmitter and receiver) and a suitable reflector, which may be a topographic feature or a retroreflector, located at either end of a path through the atmosphere to be monitored.
This Standard is also applicable when an equipment manufacturer makes any claims regarding any special features of construction or superior performance that exceed the minimum requirements of this standard. All such claims shall be verified and the test procedures should be extended or supplemented, where necessary, to verify the claimed performance. The additional tests shall be agreed between the manufacturer and the test laboratory and identified and described in the test report. 

This Standard does not apply to any of following: 

a) equipment intended to provide range resolution of gas concentration (e.g. Light direction and ranging (LIDAR))
b) equipment consisting of a passive optical receiver without a dedicated optical source
c) equipment intended to measure the local volumetric concentration of gas (point sensors) 
d) equipment intended for the detection of dusts or mists in air 
e) equipment for cross stack monitoring
f) equipment intended for the detection of explosives
g) equipment intended only for the identification of individual gas or vapour components, (e.g. Fourier transform infrared spectroscopy (FTIR))

This Standard is applicable to equipment which is intended for use in hazardous or nonhazardous areas, or both. Equipment for use in hazardous areas is also required to have explosion protection (see 4.1.1). 

This Standard applies to portable, transportable and fixed equipment intended for commercial and industrial applications. 

Note 3 This Standard is intended to provide for the supply of equipment giving a level of performance suitable for general purpose applications. However, for specific applications a prospective purchaser or an appropriate authority may additionally require equipment to be submitted for particular tests or approval. Such tests or approval are regarded as additional to and separate from the provisions of the standards referred to above.