Industrial gas detectors are designed to detect the presence of a hazardous gas at a particular fixed point in space, or across a "line of sight" between source and receiver. Either way, because they're deemed safety critical devices, they're typically hardwired—receiving power and sending signals over reliable, permanent connections. But they also can communciate wirelessly, offering a more flexible, easy to-deploy system that can also bring in signals from necessarily wireless personal gas monitors.
The first of what were proprietary wireless gas detection systems were developed for use on a "temporary" basis on drilling rigs, but transitioned to being used during maintenance work and shutdowns for locations not equipped with permanent, fixed detection systems. In such cases, the presence of workers together with altered equipment integrity results in a greater risk of exposure during maintenance than during normal operations.
Personal monitor integration
These systems can integrate the multi-gas and man-down personal monitors worn by workers, as well as stationary area monitors using a wireless self-healing mesh, star or hybrid network architecture to provide coverage over distances and equipment layouts equivalent to most process units.
The base stations also have integrated horn and light annunciation and, in some cases, extra programmable relay outputs to connect to additional local external annunciation. Because people rely on these systems, it's recommended the controller be connected to 120 VAC power. However, as with any temporary installation, the power source may be susceptible to interruption, so these units also have an integrated battery back-up system as well.
The encrypted proprietary wireless network connecting all the equipment operates at 2.4 GHz between base stations up to 300m apart, and with up to 24 devices per network group and multiple independent configurable networks to increase the total number of devices in a system.
The units have RS-485 and Ethernet connectivity with Modbus/TCP communications, and in some cases, a built-in data logger to a local SD card as a backup if the network goes down.
These protocols can be used to connect directly to your local control system at the I/O level, though this is likely more work than you might want, unless you wish to integrate your permanent and fixed annunciation systems together.
If you only require history, then it will be better to connect in the DMZ zone of your plant network using other protocols or transportation mechanisms such as Bluetooth or cellular services to transmit information to the cloud for remote integrated monitoring via a web browser.
A non-proprietary alternative
The other more familiar option for a facility's 2.4 GHz network is WirelessHART.
More than one manufacturer provides WirelessHART gas detectors with units available for H2S and LEL (methane). As with most HART-capable products, the target market for these detectors is for permanent installation, with the wireless option supporting areas with limited cable infrastructure.
Alternatively, WirelessHART gas detectors can be used in place of proprietary fixed-point detectors and be integrated into the existing annunciation system.
Regardless of which option or type of gas detection you choose, one of the most important things to consider is proper detector location (not just horizontally but also vertically), as well as awareness of limitations due to wind direction, calibration of LEL detectors with flammable gas most likely to be present, protection from dust/water, and ability to calibrate and maintain.
Just like "Big Brother" can follow your cell phone activity, web browsing, and purchasing habits, similar technologies can help keep you safe in the work environment—even during abnormal plant operations, while your cell phone is sitting safely in your locker.
About the author: Ian Verhappen
