Human beings are marvels of biological engineering. We have a supercomputer in our head that can obtain, learn and store information. We have arms that can help us to hold, carry and shape things. Legs allow us to be mobile, with built in brakes, steering and all-wheel drive. Our body acts as a fuel tank, engine and chassis all at once.

The brain, in particular, can work together with all of the parts of our body, to figure out what is going on in our world, and then work-out what appropriate course of action is needed. An example of this, is using our nose. Some are pointy, some are round, some are big, some are small, but whatever nose you have, they all serve two purposes:

  • The intake of air to allow oxygen to enter our body through the mechanism of breathing
  • The ability to “smell” – another clever means by which, at a very base-instinct level, we humans can possibly detect any signs of trouble

Can you smell burning whilst laying comfortably in bed? That could be an ominous sign of a life-threatening fire developing in your home. Can you smell petrol while driving your car? Maybe a fuel line has split, you had better pull over before you skid on the leaking fuel, or a fire starts. Is that a wonderful, sweet smelling aroma entering your nostrils? Maybe it was the scent being worn by the person who just walked past you, giving you a polite but cheeky grin. What on earth am I rambling on about, though? And more importantly, does any of this have anything to do with gas testing/detection in the workplace? Yes, absolutely it does. So first, let us look at what gas is, and why we should not just rely on our nose to get us out of trouble.

“gas can be formed through industrial processes, chemical reactions, or naturally occurring in the environment around us”

What a state

There are many states of matter in our world, the most common three being solids, liquids and gasses. There are many others including mists, dusts, fumes and so on, but we will focus on gasses for this article. Gas can be formed through industrial processes, chemical reactions, or may simply be naturally occurring in the environment around us. Heating and cooking in the home, welding, grinding and purging are just a few of the myriad uses we have for them. One of the main issues we are going to have when trying to rely on our nose, is that some gasses are undetectable to humans, presenting major risks.


Let us take Carbon Monoxide (CO) gas as an example. In many parts of the world, people have water and heating systems that use this gas to heat their showers and baths, and their homes in general. The major issue here is that this gas has no taste or smell and cannot be seen (as it has no colour). On many occasions, death has occurred whilst people are sleeping, through asphyxiation. They have no idea that they are being poisoned, as they have no clue that there is a CO leak.


Flammability of gasses is another major issue. Fires and/or explosions are a risk, especially when performing hot works (such as welding or grinding.) Another concern is that some gasses are heavier than air, which means that they collect in low-lying areas such as trenches, pits and wells. The danger here is that they will often be undetected, through improperly testing for the gas, or simply due to the fact that no one has any idea it is there in the first place. Other dangers include the acute (short-term) and Chronic (log-term) ill-health effects that may be caused to our colleagues; spreading of gas to vulnerable areas (such as schools, homes, parks and areas where people simply do not have the ability to deal with the problem); and other adverse effects of gas being released into the natural environment (acid rain, pollution of groundwater and toxic air, just to name a few).

““the nose, knows” purely relying on it would be folly. This is where gas testing/detection and monitoring comes in”

Oxygen enrichment

Even gasses such as oxygen, which to the layman are harmless, can be of great danger to human life. Without Oxygen, or not having enough of it (Oxygen Deficiency) we cannot survive. Having excess Oxygen (Oxygen Enrichment) can also be extremely dangerous through increased fire risks (Oxygen is one of the three key elements of the Fire Triangle, the other two being Fuel and a source of Heat/Ignition). Severe health effects, such as oxygen toxicity, can also occur. So, whilst the saying goes “The Nose, Knows” (a bit of a tongue-twister there!), purely relying on it would be folly. This is where gas testing/detection and monitoring comes in.

There are many different types of gas testing/detection and gas monitoring systems and regimes, and what exactly is needed depends upon the exact circumstances of the work involved, and the working environment in general. In some circumstances, we may only need to perform an initial test to see if a gas is present. Several tests for several different types of gas may be needed on other occasions. In cases where gas may always be present in the work area, performing one test would simply not be adequate, so constant monitoring would be required in this case.

Gas levels can fluctuate randomly between harmless and dangerous levels, which is the reason why we have units of measurement such as:

1. LEL (Lower Explosive Limits) and UEL (Upper Explosive Limits), which allow you to see if a gas is in sufficient quantity to cause a fire and/or explosion. Gasses below their LEL will not ignite, as there is too much air (the mixture of air/gas is to lean). Gasses above their UEL will also not ignite, as there is too much fuel. (the mixture of air/gas is too rich).

2. STEL (Short-Term Exposure Limit), LTEL (long-Term Exposure Limit), TWA (Time Weighted Average), OEL (Occupational Exposure Limit), WEL (Workplace Exposure Limit), and PEL (Personal Exposure Limit) amongst others, are the maximum amount of airborne substance our colleagues can legally be exposed to (NOTE: exactly what acronyms and terms you use, would depend on your local jurisdiction and the laws there. Also, these terms not only apply to gasses, but other substances such as airborne dusts).

A suitable and sufficient risk assessment for the particular tasks or work area you are in, is key to successfully developing the particular Testing/Detection and Monitoring regime you need for your particular circumstances. Again, due to the varied nature and effects of gasses, you must ensure the persons developing these systems are competent. If you are not sure, or have any doubts at all, seek expert advice and assistance. There are plenty of Consultants and Specialists you can approach about this topic. Maybe even speak to your local Health and Safety Enforcing Authority (examples include the UK’s “HSE – Health & Safety Executive” and the USA’s “OSHA – Occupational Safety & Health Administration”). Remember, they are not just there to punish those companies who break the law, they are also there for help, advice and information.

Detection or monitoring?

So, what is the difference between gas testing/detection, and gas monitoring? Well, gas testing is a proactive control measure. Any presence of gasses is looked for by using some type of equipment or device to measure the levels of gas in a certain area. Usually this is done before any work has started, but can be done during and after work also, depending upon the circumstances (e.g., checking for leaks around
a joint to see if welding has been done correctly).

Gas monitoring is more of a reactive measure. Fixed systems on plant and equipment are used to constantly check the environment around the equipment to see what gasses are present and at what levels. If the level of gasses becomes dangerous, these systems are usually alarmed in some way, to warn the workforce of the potential danger.

Other systems can also be worn by the personnel themselves, to monitor their breathing zone (mouth and nose). Whether it be using the devices, installing and maintaining them, or training people in their use, all workers involved in this process must be competent. Any miscalculation or misunderstanding can lead to disaster.


An example of the kind of error that may occur could result from something called “Stratification”. Stratification is different gasses being at different levels of the same environment, as some are heavier than others. For example, a space may contain H2S gas. This gas is heavier than air, so will accumulate at the bottom of the space, whilst any other gasses present will sit above it. So, if our authorised gas tester is not competent, they may only check the top half of the space, and think it is safe to enter and work in/around. A competent gas tester would test the entire space, at all levels, detecting the presence of the H2S and therefore saving lives, by ensuring the space was purged and vented, re-testing the space afterwards to ensure all the H2S had been removed before any work started. The area around the space would also be tested, to ensure the hazardous gas was not leaking out somewhere. This is especially important for working in and around confined spaces, as many people think it is only dangerous to work inside the confined space, when in reality, the area around the confined space might also be dangerous.

Testing and monitoring equipment is very sensitive, and therefore should be calibrated correctly for the job at hand. If this is not done, it can present a problem, as we then get incorrect results. This will lead to us making incorrect decisions about the safety of an area, particularly if those results show “safe” levels of gas. Competence of the workforce is also a critical factor when it comes to working safely with gasses.

If workers are not trained on the dangers of these gasses (or just as bad, are trained poorly/incorrectly), how can they possibly know what the safe levels of gas are, how to react to information provided by the equipment, and what to do in an emergency. Incidents at Shah Field in the UAE in 2009 (H2S, three killed, one injured) and Valero Refinery, Delaware, USA on November 6, 2005 (Nitrogen, two killed. show just how important training is to the whole process.

Getting the right equipment

The equipment itself can come in many different forms, and what is right for your business and workplace depends upon your circumstances. A gas tube sampling system may be enough if you are only looking for relatively small quantities of one particular gas. This is simply a hand-held pump, with a glass tube inserted into the end of it. A person holds the pump in one hand, and the pump handle in the other. By pulling the handle all the way back, they draw in a sample of air from the space/atmosphere into the tube.

A reactive element or reagent will then change colour if a gas is present, showing the user how much gas there is, through a measurement scale marked on the tube. These systems are relatively easy to handle and use, require a minimum amount of training, and are relatively low cost compared to other solutions. As they have no electrical parts, they also have the added advantage of not being a fire risk, as they are not spark or heat producing. Like anything in life however, they do have limitations. The tubes are normally specifically designed to detect one type of gas, so several different tube types would be required to test for several different gasses. These tubes can also break very easily. As they require a person to hold them and pull a handle to use them, this presents problems if trying to test large spaces, as the person testing for gas can only test places they can physically reach. Sampling tubes will also only tell us the amount of gas present at that very moment in time, and cannot do constant monitoring of the air. This is because once a sample is taken, the tube has to be replaced with a new one.

A multi-gas detector is ideal if you need to test for multiple types of gas. There are manufacturers all over the world who make these pieces of equipment, suited to specific industries or for more general applications. multi-gas detectors test and monitor the air around them. Unlike a sampling tube, these testing and detection systems can be fixed to certain areas of plant or equipment. They are also able to test varying levels of an atmosphere, without putting the user at risk. For example, a gas tester may be using a device with a long tube attached to it. The tube can be lowered into the atmosphere to be tested, without any workers having to physically entering the space themselves.

Another advantage these machines have is that they can instantly alert people to danger. Audible alarms, lights, and readings on a visual display all inform the user/wearer of the danger present. This alert will happen at one of the levels we discussed earlier (Wels, TWA and so on), allowing workers to escape to a place of safety, before it becomes too dangerous for them. This “real-time” monitoring of the air also allows for accurate measurement of potentially fluctuating gas levels.

Monitoring can also be done through the use of personal monitors, usually being positioned around the breathing zone of the individual. These are particularly useful when gas testing is intermittent, and as a contingency in case there are issues with other gas testing and monitoring systems. They are also useful for investigating where potential leaks may occur. A group of workers may be working together in a specific area, but only one or two of them are exposed to the hazardous gas, indicated to us by the fact their monitors “go off” but none of the others do. Personal monitors are also useful for monitoring the health of workers, as all of us are different in terms of the amount of a substance we can be exposed to, and for how long (individual susceptibility).

However, all of these systems can present issues. Without correct training, they can be very complicated to use (although this risk can be eliminated or minimised by one-button operation machines). Regular maintenance and calibration is also key to ensure that we being given a correct reading of the gasses present. Equipment in workplaces that present a fire or explosion hazard, must be “intrinsically safe”, designed in such a way that their use will not cause flammable gasses to ignite. The markings on them, such as (EX) or ATEX, will indicate this. The portable versions of these systems can have issues all on their own, with batteries running out, and equipment being damaged through rough use or being dropped. Another big issue is the potential for accidental or deliberate misuse. Forgetting to wear them, or wearing them in a totally inappropriate place, or forgetting to turn them on are common issues. A Monitor worn on a hard hat or hip pocket can easily be knocked off the body, and it would be difficult to know if it had activated when placed onto that body position. Using the wrong type of equipment could also mean hazardous gasses go undetected.

It is important to remember that gas monitors are a “Mitigation” device, they will not prevent the release or presence of gas, only inform us it is suddenly there. As per the hierarchy of controls, eliminating the gas is the best way to be risk-free. At the very least though, gas testing can give us an indication of any potential problem before work starts, hopefully preventing many gas related incidents and accidents from occurring in the first place. As stated in a previous article I have written on this topic, there plenty of examples of incidents involving gasses and gas testing on the USCSB (United States Chemical Safety Board) official website and YouTube pages (, ).


As always, risk assessing your workplace and tasks will give you the key information in developing the correct strategies in dealing with the hazards posed by gasses, and incorrect gas detection/testing and monitoring. Consideration of other control measures should also be taken into account. Can you do the work without using the gas? Can you replace the gas with another that is less hazardous? Is there a time when the gas is at safer levels than other times?

Information, instruction and training to everyone who may be potentially affected by your work with gas, not just your workforce, will help allow implementation of effective Emergency arrangements, so everyone is prepared, should the worst-case scenario be realized. Sniff out the danger, so you can protect your colleagues, friends and everyone else, from the risks posed by hazardous gasses.