Single gas detectors, often referred to as personal gas monitors have been in service for quite a number of years. They are a regular every day sight attached to worker’s coveralls in a wide range of industries and accepted as part of the uniform much like the company badge on the very same pair of coveralls. Whether they are black, yellow, orange or blue they all perform much the same function, don’t they?
There is still a wide misconception that these single gas devices are ‘maintenance free’ and will work for two to three years before having to be replaced without the need for any intervention in terms of service or testing. This is of course incorrect and a potentially very dangerous view.
Given the fact that hydrogen sulphide (H2S) which is a very common contaminant in the oil industry can kill at exposures of less than a minute when in concentrations as low as 0.05% (500ppm) most people would agree that it is extremely important to have a gas detector that is working correctly and efficiently. The current levels for H2S of 5ppm and 10ppm (in the UK) for warning and danger alarms demonstrate how finely tuned a personal gas detector is and keeping these devices running correctly is an important responsibility.
The majority of mass produced single gas personal detectors which are the most commonly found on oil and gas sites utilise chemically based sensors which require testing regularly throughout their service life. Failure to carry out the required testing can result in a significant number of devices being rendered completely useless which places workers in potentially dangerous and life threatening situations. Of course with a clear and simple management system in place dangerous situations can be avoided, workers can benefit from peace of mind and managers and business? owners can rest easy in the fact that their statutory obligations have been fulfilled.
The majority of single gas detectors in use in the oil and gas industries are manufactured by a relatively small number of companies which include BW Technologies and Sperian Instrumentation (both part of the Honeywell Group), Industrial Scientific, MSA, Crowcon, RAE Systems and Draeger.
Generally the greatest volume of units that are mass issued to employees incorporate the electro-chemical sensors. Due to the sheer number of this type of unit currently in service it is this type that this article will focus on particularly the H2S detectors used widely in the oil industry.
Manufacturers advice on bump testing
Most manufacturers stipulate that personal gas detectors be bump tested prior to each day’s use by the employee. Currently different sites and companies have widely differing policies on this ranging from the manufacturer’s recommendation of testing each day through to any time within three months. There must also be companies that have no policy at all in place which is the most concerning. It is ironic to think that multi gas detectors (which generally use the same type of sensors) are accepted as equipment that must be regularly calibrated with end users checking for calibration stickers on their units and requesting copies of calibration certificates before committing to a particular activity such as confined space entry.
Bump testing (and usually calibration) can be carried out either manually or automatically depending on the system being used. Manual bump test testing will generally use a free flowing sample gas of a set concentration for H2S devices this is generally somewhere around 25ppm (0.0025%) and can be carried out virtually anywhere as it does not require any special equipment. Whilst manual testing is achievable anywhere it does have major drawbacks in that it takes much longer to bump test a single device, only a single device can be reasonably bump tested at a time by one person and all records will have to be created manually. Of course if you have only a small number of devices to manage this method is entirely acceptable.
Automatic bump testing will normally utilise a bump test and calibration station designed by the equipment manufacturer and is more simple in it’s operation which generally allows a wider range of operators to use the machine indeed in many cases this will include all users. Automatic stations will store all of the bump test, calibration and event log data which is then transferred either manually or in some cases automatically to a master database. In addition it is possible to link up to four or five bump test stations to a single cylinder of test gas which allows greater numbers of devices to be tested simultaneously.