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.

Automatic stations use only a measured amount of test gas for each device which significantly reduces the on-going cost of testing. It is important that bump testing is carried out with a small measured dose of the gas to be detected as high concentrations of gasses can adversely affect the performance of electro-chemical sensors and in some cases can overload them causing them to fail and need replacing.

It is no longer acceptable to simply ‘show’ a device to an unknown concentration of the gas just to prove that the device can positively detect the gas.

Bump testing in the real world

Bump testing takes time, anywhere from thirty seconds up to two minutes depending on the device and whether you utilise the manufacturer’s proprietary machine or test manually using a free flow cylinder of the required gas. Multiply this one to two minutes? (on average) by your work force on any particular day and you have a chunk of time ‘lost’ to a seemingly non productive activity. On a site with one thousand operational staff that would equate to at least twenty five hours per day (9000+ hours per year) and this doesn’t count the ‘water cooler’ conversations that inevitably take place whilst the activity is being conducted nor the lost time in queuing to use a machine.

With this amount of time being taken up most managers will look to make savings in this area by reducing the frequency of bump tests. Opting for a weekly test over a daily test will immediately reduce the time spent by as much as 85%. At the extreme end of the scale a three monthly test will reduce the time spent by nearly 99%.

Safety must however be the key concern and the unarguable fact is that the only simple way to be sure that your device is operating as it is designed to do is to carry out a bump test which uses a small sample of test gas that is passed over the sensor. Given the manufacturer’s recommendation you should aim to bump test in line with their instructions and failing that adhere as closely as you can as far as is reasonably practicable.

There is published data within the industry that states that the farther away your device is from the last bump test the less accurate it will be. Indeed in a recent study it was found that given a typical company with two thousand devices as many as 24 units have a likelihood to fail to detect gas as they were designed just thirty days from their last bump test. In addition up to three devices in one thousand can fail to detect gas as they were designed to on any given day. A device can fail to alarm due to any number of reasons which apart from the obvious possibility of a failed sensor include sensors blocked by dirt, damaged electronics due to drops from height and even following immersion in or splash by liquids. Whilst the quality and durability of modern day devices is constantly improving they are expected to work in environments of extremes of temperature and humidity and where mechanical hazards such crushing or abrasion threaten.

Record keeping

As with all good management practice, records of all bump tests must be kept whether it be stored electronically or recorded on paper. These records should include any data logs of events that have been downloaded from the devices.

One of the best approaches is to utilise the manufacturer’s bump station and management software which in most cases provides an easy to use solution ‘out of the box’. This can potentially represent a significant financial outlay for users with a small number of devices however the benefits of using an off the shelf solution are that not only is a good quality system delivered from day one it also ensures that there are no gaps in the management system. Today’s automatic bump testing machines are quite sophisticated and are usually able to calibrate, bump test and measure very accurately. The information recorded via an automatic station can be very detailed and will include the basic details of the device, details of all previous tests, sensor status, software version also user defined data.

The records kept within a good management system can be a valuable source of data with the potential to identify trends in equipment performance and also areas of a sites where there may be leaks of toxic or explosive gasses. Good interpretation of data such as sensor status can pre-empt a failing unit and prevent it from causing a problem whilst in service.

There is also the opportunity to monitor employee behaviour during alarm conditions. This data can then be used positively in a training to? highlight where there may be complacency towards device alarms which potentially could result in personnel being harmed or killed. Companies can choose to outsource their bump test and calibration record keeping to an outside company whether that be the manufacturer, outside contractor or an gas detection distributor. This can vary from simple paper record systems to full near automatic on line systems.

Site contractors

Larger scale employers (contractors) with regular day to day activity on oil and gas sites are often included within the main site’s testing and monitoring systems and are supported equally to the directly employed site staff. These employers should have access to all of the records relating to the testing and calibration of their staff’s devices including any data logs of alarm events.

There is also a small but none the less significant number of smaller size contracting companies and less regular visitors to oil and gas sites that are not included in the main site’s management system. Despite these employees being issued personal gas detectors either by their employers or their client company running the site their employer may not be aware of the importance of regular bump testing in line with the device manufacturer’s instructions.

Furthermore there is a danger in that if they are attending a site with an overly long period between bump tests they may have little or no regard for any testing or control of the devices.

It is also important to note that if the personnel of these smaller firms and less regular visitors utilise the bump test facilities provided on the main site their employer will probably not have access to any of the records that they must keep. It is this ‘being in the dark’ scenario that potentially puts workers in very dangerous situations despite those individuals believing that they are protected by a gas detector that is working efficiently.

The future

Personal gas detectors are continuing to improve in reliability and durability and are now almost all shipped with a manufacturer’s warranty covering at least two years which for the majority is the entire design life of the unit. Sensor life is increasing with some companies now offering five year warranties on H2S and other toxic electro-chemical sensors. These improvements have the potential though to allow users to become complacent about their devices so it is important to maintain a robust system of testing and recording in order to ensure that all of their in service equipment is working correctly.?

It is well worth every company that employs workers that have to use personal gas detectors periodically reviewing not only their choice of equipment but also the management system that they have in place. Indeed you could argue that the selection of equipment could be made on the effectiveness of the test stations and management software provided by the manufacturer rather than unit price of the devices alone. If testing is done ‘in house’ would it be better done by an external contractor? If a large site with many different companies present should the site owner take responsibility for all the equipment on their site or simply publish a policy for contractors and include it as part of a wider safety audit?

As with all personal protective equipment personal gas detectors are the last line of defence in any hierarchy of risk control where a hazard exists so they should be used in addition to fixed and portable area monitoring and other engineering controls. Given the fact though that there could be a failure or other issue with fixed gas detections systems personal gas detectors will probably be around for quite some time to come. With their relatively low cost of ownership and the fact that a monitor on every worker is more likely to provide a much earlier alarm there is definitely an argument that there is increased safety in numbers.

Author Details:

Mark J Smith Simon Safety & Lifting Centre Ltd

T: +44 (0)1646 600750 F: +44 (0)1646 602299

Published: 10th Apr 2011 in Health and Safety International