Gas alarm system

31 May 2016

Hydrogen Sulphide (H2S) is an odorous gas, reminiscent of rotten eggs. With an odour threshold between 0.005 ppm and 1.5ppm, relatively low levels of Hydrogen Sulphide can result in complaints if industrial plants generate exposure at these levels.

A chemical waste treatment plant in the UK has therefore installed a monitoring and alarm system to generate alerts when H2S concentrations reach levels that might cause concern with staff and the public.

A highly toxic and flammable gas, Hydrogen Sulphide can cause irritation to the eyes, throat and lungs, and can cause death in high concentrations.

The challenge for the monitoring instrumentation sector is to be able to monitor Hydrogen Sulphide at sufficiently low levels continuously without interferences from other gases. So, when Air Monitors was approached by a chemical waste treatment plant looking to install a Hydrogen Sulphide alarm system, the Honeywell SPM Flex was the obvious choice.

Colin Craggs from Air Monitors said: “The SPM Flex operates a novel cartridge system that enables users to select the specific gas or gases of interest – H2S in this case, and we connected the instrument to an Envirologger, so that data could be viewed on the web, and so that alarms can be issued in a variety of ways – email, text etc.”

With a detection limit of 1 part per billion (ppb) the SPM Flex is extremely sensitive; each cartridge contains a tape which has been impregnated with chemicals that perform analysis of the target gas. The chemical reaction that takes place produces a colorimetric response that, whilst not visible to the eye, is measured by the instrument’s internal optics.

Colin added: “The key to the success of this system is the sensitivity of the monitor; by setting the alarm level at such a low concentration the wastewater treatment plant is able to raise an alarm before staff and neighbours notice the odour, and in doing so, they ensure that potentially harmful exposure is effectively prevented.”