Catalytic sensors series 47K-ST
[received extended performance certification to EN Standards]

Flammable gas detectors offer a means for automatic and fast monitoring of an area to warn of potentially hazardous gas and vapour release. In contrast to traditional flame detectors, a flammable gas detector can alarm before an ignition occurs and can contribute to reduce the risk of explosion by initiating the appropriate safety action. Such action could be an automatic shut-off of gas valves, switching on ventilation fans, shutting down a process stream or just actuating audible and visual alarm devices such as horns and beacons to alert and evacuate workers.

Most flammable gas detectors employ an electrically heated catalytic element (filament), which oxidizes any combustible gas present that comes into contact with the filament surface.

The resulting increase in the temperature and resistance of the filament is sensed and amplified in an electronic circuit, which provides the gas concentration reading usually in terms of a percentage of the Lower Explosive Limit (LEL) of that specific gas or vapour.

The LEL is the minimum concentration of a vapour/gas expressed as the percentage of volume in air required to sustain a fire.

The Upper Explosive Limit (UEL) is instead the maximum concentration of a vapour/gas expressed as the percentage of volume in air beyond which a fire cannot be sustained, as the amount of oxygen would be insufficient to continue the fire.

The actual LEL and UEL level for different gases/vapours may vary widely in function of the molecular composition and physical properties of the specific substance.

LEL’s and UEL’s can be found in the EN 61779 or in the Database Chemsafe (Dechema).

Though developed almost 80 years ago, the catalytic sensor technology has advanced remarkably over the past decades and is still considered reliable with some limitations.

Advantages

• Well-proven technology
• Cost effective ownership
• Simplified installation and maintenance
• Wide range of detection of various HC’s and all flammable gases (H2, NH3.)
• 1. Flexibility with use on natural diffusion, flow-mode and duct mount sampling

Drawbacks

Detrimental effect on the catalyst as caused by certain substances:

• Poisoning effect by lead, sulphur containing compounds, phosphates, silicones, silicates, and silanes
• Inhibition effect by Hydrogen Sulphide, Halogen HC’s causing temporary loss of sensitivity, which can be recovered after a period of operation in clean air

Flammable gas detectors became fundamental following the introduction of the Directive ATEX 94/9/EC of 23rd March 1994 on the approximation of the Laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres.

This Directive is mandatory from the 1st July 2003 and it is linked to the ATEX Directive 99/92/EC concerning the minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres.

By definition of the Directive ATEX 94/9/EC, gas detectors are considered typical protective systems (safety devices) as systems featuring a measuring function capable to halt incipient explosions and /or to limit the effective range of explosion flames, as long as they are assessed as safety related devices as referred to by Directive 94/9/EC, Annex II Clause 1.5.5- 1.5.6
In order to be assessed as safety related devices with a measuring functions, the gas detectors must meet a recognised EN performance standards, which represents the experimental basis for the presumption of conformity to the Essential Safety Requirements (ESR) as set forth in the Directive.

In order to remain on the forefront of sensor research and hit the increasing market demand for compliance with the ATEX Directives, MSA Europe has implemented an ambitious programme to upgrade the catalytic gas sensors in line with the latest EN performance standards.

The catalytic sensor series 47K-ST has achieved an extended certification for as many as 32 gases and vapours according to the new performance standards EN 61779-1 and EN 61779-4 in connection with the line of MSA Controllers.

2-butanone, acetone, acetylene, ammonia, 1,3- butadiene, diethyl ether, acetic acid, acetic anhydride, ethane, ethanol, ethylene, ethyl acetate, ethylene oxide, (FAM-) Standard mineral spirit 65/95, i-butyl acetate, n-butyl acetate, n-butane, n-hexane, n-nonane, n-pentane, 2-propanol, propylene, propylene oxide, toluene, hydrogen, xylene (mixture of isomers 1:1:1 p-m-o), cyclo-pentane, allyl alcohol, i-butylene, i-butane, methanol, cyclo-hexane

The new approval for additional 32 gases and vapours as commonly found in the industrial applications has been obtained through the Notified Laboratory EXAM-PFG after extensive and successful tests and it came as a completion of the former approval obtained for Methane and Propane. For ease of use and customer’s friendly routine field calibration, relative sensitivity response factors to Propane have also been experimentally developed for each gas and vapour by the Testing House PFG. However, for the most accurate calibration and detection, a gas detector should be calibrated using the target gas/vapour as assessed by the Test House.

Now MSA Europe can offer to the market Controllers and catalytic sensors with the measuring function in the measuring range 0-100% LEL for as many as 34 gases and vapours fully performance approved to help customers improve safety at their working places and comply with the stringent requirements of the ATEX Directives in force in the EU market.

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Author:
Franco Fava
Product Manager MSA EUROPE
Phone +49 [30] 68 86 - 0
Fax +49 [30] 68 86 - 1558
E-Mail contact(at)msa-europe.com
Internet www.msa-europe.com