Using wireless in safety shower alarm retrofits
Wireless monitoring systems save money compared to wired solutions.
A chemical plant or refinery of any size has dozens to hundreds of safety shower and eyewash stations. Workers who have been splashed with or come in more direct contact with chemicals are trained to proceed to the nearest station, use the facility as necessary, and call for help using a plant radio.
While this approach works in theory, plant safety managers point to serious inadequacies:
- A worker who has been splashed by chemicals or otherwise injured may have trouble using a safety shower and a radio simultaneously.
- The ability of first responders to find the individual depends on the accuracy of the radio-location report.
- Without a radio call, there is no indication to anyone else in the facility that there has been a problem, which may extend well beyond the injury and include chemical spills or other hazards.
- Even if plants have lights and/or sirens as their main alarming system for safety showers, someone has to see or hear these.
Safety managers generally want an alarm system capable of informing operators when an incident is happening without the need for the victim to call in and report, or for another individual to witness the action and call in. The activation of a shower or eyewash station alone should be sufficient to alert operators, without requiring any further action by the victim, as well as to meet regulations and specifications, including OSHA’s 29 CFR1910.151B, ANSI Z358.1.2009, and EN 15154 in Europe.
To meet OSHA’s good practices recommendations, such as no more than four minute first-aid response in the location where the operation is in distress and no more than 15 minutes for qualified assistance, everything starts with an efficient and effective alarming system.
Companies often remain with the status quo because adding sensors connected to an alarm system using traditional wiring methods is a very expensive undertaking. Deploying a wired network of this scale is time-consuming, costly, and disruptive to daily operation during the installation process.
The practicality of using a wireless network to support safety shower sensors has increased as more companies deploy WirelessHART networks for process instruments. Where such networks already exist, it is a simple matter to add safety shower sensors. Where no wireless networks have been deployed, the initial gateway and backhaul infrastructure will have to be added, but this can in turn support wireless instrumentation.
Typical experiences comparing a wireless approach to using traditional wired sensors show the wireless cost is roughly half and the installation time is much shorter. Using a wireless network means a plant usually can achieve its safety goals at the lowest cost and within the shortest time frame, while maintaining normal production. Another important accomplishment is a more reliable and efficient monthly inspection, because the time-stamped site inspection is now digitally recorded, replacing the current process of manual notes and punching manual data in the safety system, which might add data inaccuracy.
Standard solutions for safety showers
This approach has been used often enough for shower suppliers to create the shower sensor components as a pre-packaged kit. Emerson uses an assembly consisting of a Rosemount 702 two-input discrete WirelessHART transmitter to outfit a typical safety shower and eyewash station and TopWorx magnetic proximity sensors (Figure 1). Each station needs its own assembly, and the WirelessHART transmitter communicates to the gateway serving as the collection point for the wireless transmitter data transmission.
Before the installation, a walk-through of each shower/eyewash installation can be used to determine the relative positions of the stations and transmitter mounting options to ensure each has an appropriate line-of-sight. This will ensure formation of a strong network with multiple communication paths, thanks to a mesh network topology, to ensure reliable communication. In some cases, it might be beneficial to increase the height of the transmitter with an antenna extension to provide a better sight line to other wireless devices in the network and/or to the gateway.
Adding the hardware and setting up the transmitters on the WirelessHART network is only the beginning of creating a comprehensive program. To get to the point where activation of either the shower or eyewash activates an alarm in the control room or security room, where one or more people are on duty 24/7, requires the implementation of corresponding safety and work procedures.
In a typical setup, the WirelessHART transmitters at each of the stations communicate to a gateway mounted in a central location. The gateway typically is located close to the main control room, and it always is hardwired to the DCS or other automation system. System status should be shown on a new human-machine interface (HMI) screen, added as part of the project. If there are multiple control rooms, the central location should be staffed 24/7.
The new HMI typically shows a diagram of the plant and the locations of the shower/eyewash stations. Each station should be represented on the screen using an appropriate graphic. Each transmitter on the network sends a “heartbeat” to the system showing it is working, along with basic diagnostic information such as battery condition. If a shower or eyewash handle is pulled, an alarm should sound and screen graphics should supply a clear indication of the station’s location.
Safety shower station alarms normally are treated the same as a high-priority process alarm. The operator in the control room should send out a broadcast message immediately to all radios. Unless there is an immediate response indicating the situation is under control, individuals in the plant who are trained as first responders should have standing orders to drop whatever they’re doing and provide assistance.
As an additional safety measure, once activated, the shower/eyewash alarm must be reset at the magnetic proximity sensor using a ferromagnetic key.
An integrated approach
Tackling a project like this requires the involvement of many groups within a facility including those overseeing safety and plant work practices, along with operators, maintenance, instrumentation, network management and plant management—and the wireless hardware supplier and possibly an outside integrator. The needs and concerns of all must be addressed and accommodated as well as possible. These projects also should provide opportunities to make other smaller improvements, such as insulating station header pipes where necessary.
Successful efforts such as these can positively influence planning for subsequent improvements throughout a plant. One successful project can provide new tools and practices, setting the groundwork for the next wireless installation.
Alex Patterson and Marcio Donnangelo are with Emerson Automation Solutions.