What Are the Different Types of 4 Gas Monitors?

The majority of 4 gas monitors fall into the portable category. These are enclosed units with 4 sensors that 4 gas monitor can be clipped to your body to provide continuous personal protection.

4 Gas Monitor with a Pump for Point Sampling
This type of 4 gas monitor contains a built-in or external pump. A probe is used to enable point sampling. Before entering a confined space, a sample can be drawn for analysis while the user remains in a safe location. These devices are also useful to track down toxic sources and access hard-to-reach locations.

4 Gas Monitor for Stationary Fixed Wall
The fixed wall mounted 4 gas monitor units provide continuous protection at a stationary location. These units are more expensive and offer protection in a localized indoor space, such as an engine room or industrial factory setting. Fixed wall 4 gas monitors are also useful in confined spaces with heavy occupational traffic, like a mining shaft.

How Do 4 Gas Sensors Work?
A 4 gas monitor is composed of electronics and four sensors. The gas sensors convert the detected gas concentration to an electronic signal for analysis by the on-board microprocessor. From there, the processor outputs the reading to the display screen. If the readings exceed the pre-set alarm values, the alarms will be triggered to warn the user.

As the name suggests, there are four sensors used in a 4 gas monitor. The O2, H2S, and CO sensors are electrochemical cells. The combustibles sensor reading %LEL is most often recorded by a catalytic bead pellistor sensor.

Is Using a 4 Gas Monitor Mandatory?
In certain occupational situations, a 4 gas monitor is mandatory. Several OSHA standards require the use of multi-gas monitors.

Permit-required confined spaces: paragraph (c)(5)(ii)(C) of 29 CFR 1910.146, see here.
Hazardous waste operations and emergency response: paragraph (c)(6) of 29 CFR 1910.120 (Hazardous Waste Operations and Emergency Response), see here.
Grain Handling Facilities: Section 5 (Entry Into Bins, Silos, and Tanks) in Appendix A of 29 CFR 1910.272, see here.