We all know that pellistor sensors are one of the primary technologies for detecting hydrocarbons.  In most circumstances, they’re a reliable, cost-effective means of monitoring flammable levels of combustible gases.

As with any technology, there are some circumstances in which pellistors shouldn’t be relied on, and other sensors, like infrared (IR) technology, should be considered.

Problems with pellistors

Pellistors are generally extremely reliable at detecting flammable gases.  However, every type of technology has its limits, and there are a few occasions where pellistors shouldn’t be assumed to be most suitable.

Perhaps the biggest drawback of pellistors is that they’re susceptible to poisoning (irreversible loss of sensitivity) or inhibition (reversible loss of sensitivity) by many chemicals found in related industries.

What happens when a pellistor is poisoned?

Basically, a poisoned pellistor produces no output when exposed to flammable gas. This means a detector would not go into alarm, giving the impression that the environment was safe.

Compounds containing silicon, lead, sulphur, and phosphates at just a few parts per million (ppm) can impair pellistor performance.  So whether it’s something in your general working environment, or something as innocuous as cleaning equipment or hand cream, you could be compromising your sensor’s effectiveness without even realising it.

What’s so bad about silicons?

Silicons have their virtues, but they may be more prevalent than you think; including sealants, adhesives, lubricants, and thermal and electrical insulation. They can poison pellistor sensors at extremely low levels.  For example, there was an incident where a company replaced a window pane in a room where they stored their gas detection equipment.  A standard silicon-based sealant was used in the process, and as a result all of their pellistor sensors failed their subsequent testing.  Fortunately this company tested their equipment regularly; it would have been a very different and more tragic story had they not done so.

Situations like this ably demonstrate the importance of bump testing (we’re written about it previously – take a look), which highlights poisoned or inhibited sensors.

What can I do to avoid poisoning my sensor?

Be aware, in essence –bump-test your equipment regularly, and make sure your detectors are suited to the environment you’re working in.

Find out more about infra-red technology in our previous blog.