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Confined space entry gas monitors are used on a regular basis across almost all industries; be it construction, demolition, facilities maintenance, land remediation or utility services. However, the misnomer, ‘confined space entry monitor’ or ‘confined space atmosphere tester’ is often used; but do we know what we are truly testing for?
Your run of the mill ‘confined space entry monitor' will monitor for the absence or presence of methane gas at explosive levels, oxygen, hydrogen sulfide and carbon monoxide; which is great if those are the only risks present. Nevertheless, we need to probe a little bit deeper to understand what we actually need!
When we monitor a confined space atmosphere we need to determine both prior and during occupation of the confined space, whether there is enough oxygen to breathe (too much oxygen is also a problem!), if the atmosphere is explosive or contains toxic gases/vapours that threaten your health or life!
What should I be looking for?
The choice of monitoring equipment is expansive, but we must always keep in mind what it is that we are trying to achieve. We need to ask ourselves the following:
Do I need ATEX certification and if so what zone classification do I need?
How am I going to take a sample from my confined spaces’ atmosphere; do I need a pumped instrument so I can draw a sample from a distance without entering the confined space or a diffusive instrument that is easier to wear?
What contaminants or toxic compounds are present; if so, what are the short or long term health implications and at what concentrations?
Is there a potential risk of a flammable or explosive atmosphere?
If flammable gas or vapour is present, do I need to calibrate for my specific flammable gas or vapour (Paragraph 94, Confined Spaces Regulations 1997) and can my gas monitor do that?
Does my testing and calibration need to include daily operator checks for instrument response? What are the manufacturer’s recommendations on calibration and testing intervals, as I need to be in accordance with them (Paragraph 184, Confined Spaces Regulations 1997)?
So let’s look at these questions in a little more detail and attempt to cast some light!
1. ATEX Certification
ATEX certification is required if there is a risk of an explosive mixture of gases or dust present. What ATEX certification is required is often one of the least understood aspects of confined space entry monitors, by manufacturers, distributors and end users alike, all finding this requirement challenging. Its explanation is too long for this article, but it is essential that you get a monitor with the right certification. I would recommend taking the time to visit https://www.healthandsafetyatwork.com/files/ATEX-handout.pdf for a better understanding of ATEX classifications.
2. Pumped or Diffusive
This is a relatively easy one to decide on an answer. If I am at point A and I need to take a sample from point B, I need a pumped instrument. The Confined Space Entry Regulation 1997 require an atmosphere to be tested prior to entry and to do that you need a pump to draw the air sample from within the space out to the instrument. Some may argue that the instrument could be lowered into the space from a vertical opening, however this is a little bit difficult if the area is accessed through a horizontal port. However, if I am inside a confined space and continuing to monitor the atmosphere I would then be able to use something diffusive that can be worn.
3. Types of Gas or Vapour to be Monitored
Tempting as it is, we cannot always use an off the shelf four gas monitor with the standard gases of O2, H2S, CO and LEL. We need to understand what is likely to be present in our atmosphere and be testing for that. So if I have a risk of low oxygen, chlorine, ammonia and sulphur dioxide, I need to have a gas monitor or equipment to test for oxygen, chlorine, ammonia and sulfur dioxide. Alternatively, if the risk is only low oxygen and explosive levels of methane, then I need only look for low oxygen and explosive levels of methane. It is also good practice to understand cross sensitivities of these sensors. For example, a carbon monoxide sensor is cross sensitive to hydrogen gas and certain types of organic vapours/solvents.
4. Flammable or Explosive Atmospheres
If there is potential for a flammable or explosive atmosphere then you will need something that is able to monitor lower explosive limit (LEL) values. But be aware, there are several different methods of measuring LEL. Catalytic sensors are most common, least expensive and can monitor the broadest ranges of organics. However silanes, silicones, silcates, tetraethyl lead, halogenated compounds e.g. HCl or HF, sulfur compounds, phosphate esters and nitro compounds attack and degrade catalytic sensors very quickly. The alternatives are infrared LEL or PID sensors. Infrared LEL is a superior technology to catalytic and is less susceptible to poisoning but does have the drawbacks of not being able to detect hydrogen and significantly reduced sensitivity to alkenes or alkynes. Although advertised as being able to take LEL measurements, PID sensor are not suitable for this application.
5. Calibrating specifically for the Explosive Gas
The most common mistake when deciding upon a confined space entry monitor is not taking into account that different gases or vapours have reach explosive mixtures at differing concentrations. So, if you are not looking for LEL of methane, it is necessary to either re-calibrate the monitor to the gas/vapour of interest or apply a LEL correction factor. The latter is the better option for those who are often coming across confined spaces with different explosive gases present, with the ability to dial in a correction factor being much more practical than re-calibrating a monitor to the specific gas (however this is better practice). Although slightly more expensive I would always go for a monitor that has the ability to apply LEL correction factors.
6. Operator Checks and Daily Gas Testing
This is equipment that you are entrusting your life to, would you not want to check that it is working correctly every time you use it. Ease of checking performance is essential. In order to ascertain that the gas monitor is working correctly it needs to be challenged with a known concentration of gas (a bump check) that it is trying to detect. Bump checks are almost always recommended by every manufacturer as part of a daily check. They form part of the manufacturers recommended tests and checks. As such, under Paragraph 184 of the Confined Spaces Regulations 1997, these checks become mandatory and should be undertaken before use. This is the most neglected/ignored aspect of all confined space entry monitors, often being viewed as an unnecessary expense. If it were me, I would be following this procedure religiously, who’s to know what has happened to that gas monitor since the last time you used it.
There are many confined space entry monitors out there, but when I take all of the above into consideration, I can only recommend one that comes out head and shoulders above the rest - the QRAE3. It is configurable as diffusive or pumped, not only has the standard 4 gas configuration but also sensors for sulphur dioxide, ammonia, hydrogen cyanide, phosphine, chlorine and nitrogen dioxide. Combine this with a LEL sensor with correction factor adjustment and a flawless bump/calibration station; its unbeatable. Nevertheless, its not for everyone!
I hope that this short article has been useful for you. It is by no means comprehensive, but should point you in the right direction. I would always recommend seeking specialist advise from a competent person.
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