Temperature / Wireless / Vibration

Wireless Sensors Part of Tools Used to Keep a Facility Safe

Not Part of Traditional Process Safety Systems, Wireless Sensors Keep Facility Within Design Constraints and Safe

By Ian Verhappen

I don't believe that direct use of wireless for safety systems or shutdown logic is happening to any degree at present in the process industries, but that doesn't mean wireless isn't contributing to a safer work environment. Most wireless safety applications are contributing through increased health, safety and environment (HSE)-related monitoring activities.

One of the early documented uses of wireless sensor networks was for monitoring eyewash stations and safety showers to be sure they were in a state of readiness, and that when they were activated, per OSHA requirements, notification was received in the central control room within 10 seconds of the event. Another example is monitoring fire extinguishers to confirm that they're in place and unobstructed, so that in the event they're needed, they can be easily found, and then replaced when discharged.

Wireless has been used for many years for asset tracking of equipment and people. Using gateways or cellular tower triangulation, it is possible to provide real-time tracking within meters of people's locations in a facility. Knowing who is where is an important consideration in the event of an abnormal situation, so that everyone can be accounted for or quickly located by emergency responders. The same badges used for monitoring location also can incorporate accelerometers and other technologies at a relatively minor incremental cost to monitor rapid motion (fall detection) or no motion (i.e., being in one location for too long), which would be a "man down” indication. Also, just like the "first responder” bracelets used in our homes, these systems can incorporate an emergency button to call for help yourself.

The same badges used to monitor location can have accelerometers to monitor rapid motion (fall detection) or no motion.

Monitoring people is one component of a safe environment, but preventing or alerting of potential incidents in advance is a better alternative. Most processing facilities have areas with the potential for hazardous gases or low oxygen levels, and the most common way to monitor these environments is with gas detection systems, both fixed and, recently, by creating mesh networks using the personal gas detectors worn by plant operators. This combination of fixed or permanently mounted (wired or wireless devices) in likely areas of gas emission with the personal gas detectors of operators and the ones required for field work significantly improves the coverage of a facility to detect potential incidents as early as possible, especially during the potentially higher risk associated with maintenance work.

Another controlled abnormal situation that should be monitored is a facility's safety relief valve or pressure safety valve (PSV) system. In addition to annunciating an actuation event so the facility knows the source and type of fluid entering the flare system, and indicating the vessels/process in upset condition to confirm information from other sources, the sensor also typically monitors for leaks or partial opening that may indicate other faults that could affect the integrity of the system.

Wireless monitoring of conventional process sensors such as pressure, temperature, level and vibration help keep the facility within its design constraints, also contributing to the safe, reliable operation of the facility.

Wireless networks are being used in HSE applications and, to some extent, to capture diagnostic information from safety systems in which the control signals are analog. The diagnostics are transmitted in a parallel network so they can be used for improved probability of failure on demand coverage.

Work on wireless for safety applications is ongoing. ISA84 WG8 is preparing a technical report, "Guidance for Application of Wireless Sensor Technology for Non-SIS Independent Protection Layers,” that will help users learn how to make effective use of wireless in more direct process safety protection applications.

Wireless sensors may not yet be part of traditional process safety systems, but they certainly are part of the suite of tools used to keep a facility safe.