Potential hazards associated with gas sampling systems

Certain precautions must be taken to ensure that the area in which gas sampling equipment is sited is not made hazardous. The various circumstances that can give rise to such a situation occurring can be complex and the precautions must cover every eventuality. The alternative is to extend the hazardous area to include the site where the equipment is positioned and to manufacture the equipment to conform to an acceptable standard of certification such as Ex ´p´, or ensure that all electrical components are either flameproof or intrinsically safe. This can become very expensive and restrictive and is not acceptable to users whose experience of the concept of Zones and Certified Equipment may be very limited. Two typical applications of this concept are the monitoring of digester gas and of landfill gases. The authors discuss these applications. They describe the digester gas sampling system and discuss fault conditions, safety control, sequential sampling and dual fault conditions