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Choosing the Best Confined Space Gas Sniffer

Two common questions we get are: What are the differences between the various gas sniffers that are available? Which gas sniffer should I use for my confined space entry application?


There are two differences that are most relevant for the average application. The two differences are (1) Power Source, and (2) Sampling Method.

Power Source

Currently, confined space gas monitors come in two power source configurations - alkaline battery powered or rechargeable lithium battery powered.

The question to ask is how do you plan on using your gas sniffer?

BW GasAlert MicroClip XLIf you will use it everyday, the rechargeable versions may be a better choice. Simply charge the sniffer after each use and it'll be ready for the next work day. This will also save you money on the purchase of alkaline batteries. On most monitors, a full charge will get you about 10-12 hours of use.

GFG G450 Confined Space Gas DetectorIf you will use your gas detector as jobs arise or infrequently, the alkaline battery monitors will prove to be more convenient. You don't have to remember to charge the detector. You don't have to keep up with a charger - just pop in a few batteries and your ready to go.

Note that there are a few disposable gas monitors on the market that never need charging - like the MGC-Simple. Generally, you turn them on (they never turn off) and they run for two years (sometimes three) and then expire. Typically, these instruments are not repairable.

Sampling Method

Confined space gas monitors detect dangerous atmospheres by one of two ways: sample draw testing or diffusion testing. There are pluses and minuses to both methods.

BW GasAlert Max XT IISample draw testing is usually accomplished via a pump located inside the gas detector. Often times, a pump module can also be added to a diffusion monitor. The advantage to this method is that it allows for a much easier way to remote test a confined space before entry. One simply lowers the sample tube into the space.

There are at least two disadvantages to this method of sampling.

The first one is that pumps will draw air from the point of least resistance. This means that if there is a small compromise of the sampling system within the meter itself, there is a possibility the air that's being sampled is the topside air.

The other disadvantage is the way the remote sampling must be done. An accurate sample requires that the end of the sample tube remain still for 1-2 seconds for every foot of sampling tube being used.

This means that in order to test different layers of the space's atmosphere (as you should do), you'll have to drop the tube down a few feet, hold for 10-20 seconds, and then repeat.

OSHA, by the way, does require that you test the different layers of a space. They say, "When monitoring for entries involving a descent into atmospheres that may be stratified, the atmospheric envelope should be tested a distance of approximately 4 feet (1.22 m) in the direction of travel and to each side. If a sampling probe is used, the entrant's rate of progress should be slowed to accommodate the sampling speed and detector response."

BW Quattro Confined Space Gas SnifferDiffusion testing simply refers to sampling the air that naturally diffuses over the sensors at the meter itself. The advantage of this method is you don't have to keep up with pump maintenance, filters, the threat of sucking up water, etc.

The disadvantage is that to test a confined space remotely before entry, you'll have to tie a rope to the gas detector and lower it down into the space.

However, when remote sampling this way, you only need to keep the monitor at a certain layer of the confined space's atmosphere for a couple of seconds to get an accurate sample.

Miscellaneous Differences

All confined space sniffers carry long warranties nowadays - 2-3 years usually. Most are usually programmable in some fashion. Some have "bells and whistle" add-ons that are usually designed to set themselves apart but don't offer any significant advantages.

The BW Max XT II does have a unique feature that actually is quite valuable. It can sample remotely via its internal pump, OR it can be turned into a diffusion monitor. This gives you the best of both worlds.

We have found that some gas sniffers really are more rugged and durable than others. While all the monitors we sell are durable, the GFG G450 gas monitor has proven to be extremely durable.


Hopefully, you now have enough information to make an informed choice. In our experience, contractors have gravitated towards diffusion monitors that run on alkaline batteries. Those who use monitors every day gravitate towards the rechargeable models. All of this is certainly not a hard and fast rule. Ultimately, it comes down to personal preference.

Whichever model you buy, do not buy it from a big box online seller. Why? Although you might save a few bucks up front, good luck getting your monitor calibrated, repaired, or serviced under warranty. We do all of those things at our in-house repair center in a matter of days. We've been at this for over 45 years, we know what we're doing.

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