Conceptual Design Considerations for Emergency Warning Systems
June 1, 2007 By Pulp & Paper Canada
While it is clear that fire alarms are required and that most people have an understanding of their function and purpose, industrial facilities are subject to many other types of emergencies. These in…
While it is clear that fire alarms are required and that most people have an understanding of their function and purpose, industrial facilities are subject to many other types of emergencies. These include gas releases, spills, emergency shutdowns, weather (such as tornadoes), terrorism threats, and many others.
These emergencies might require responses that are either localized, plant-wide or even cover the greater community. Some emergencies require evacuation; others may require sheltering in situ. Emergencies obviously have higher priority than “regular” communication and different emergencies may have different priorities. This leads to the requirement for “emergency communication systems” and “automated warning systems” but what might they look like? Is a single-tone air horn good enough? What about radios? Can a multi-tone generator be used to cover the multiple types of emergencies which may occur? What about multiple coloured flashing lights? What about a combination of all of these?
Each facility requires a different type of emergency warning system in order to address the various types of emergencies and responses required. As indicated by the legislative requirements outlined previously (PPC, May 2007), a single-tone air horn is inadequate to provide proper notification to personnel in most circumstances. Radios are often considered to meet the requirements for emergency warning systems, but in fact, they have many limitations. These include dead batteries, contractors and visitors not being issued with radios, coverage limitations due to large metal structures and enclosures, high ambient noise levels, lack of security from eavesdroppers and terrorists, system-wide failure due to “keyed” microphones, and a lack of disciplined communication during an emergency.
Multi-tone generators add some flexibility during emergencies but, as stated earlier, confusion can be created if the tones are similar to one another. The problems are threefold. The first is identifying what the tone means and, secondly, what the correct response is. Finally, how are personnel notified if the required response is non-standard? The problems are accentuated for new hires and visitors who may not have a complete knowledge of how to respond to the tones.
Various coloured strobe lights help, but have many of the same limitations as the multi-tone generators.
So what does a good emergency warning system consist of? Following the recommendations of NFPA 72 Annex E, the system should be designed by a person specifically trained in such design and implementation. It must meet the requirements of the legislation of the jurisdiction having authority. It must meet the intentions of the corporate HS&E policy, as well as industry standards and good engineering practices.
It is recommended that the fire alarm system be integrated into the emergency warning system. The emergency warning system should consist of a library of speech messages, with specific messages output according to the specific input device(s). In unusual (unforeseen) circumstances, emergency personnel should be able to provide special instructions by overriding the automatic functions of the emergency warning system. A pre-tone should be broadcast prior to the speech instructions. This provides a “heads up” that there is an emergency, and that detailed instructions are about to be given. Personnel can then think about what they are to do, and act accordingly, based on a full understanding of the message. Activation of strobe lights will enhance the pre-tone warning. During an emergency, it is imperative that communication between emergency personnel and others be disciplined. In order that instructions be clearly understood, only one party can speak at a time. It is up to emergency service personnel to determine who can speak and when. The emergency warning system must accommodate this function.
From a technical standpoint, the emergency warning system should be completely self-monitoring. This functionality is critical to ensure that the system works when it is required to work. The EWS can actually become a liability if it does not work as expected during a crisis situation. Manual monthly tests are also required, with activation by different devices on consecutive tests. This ensures that even if the self-monitoring function fails, other component failures will be found. All components should be monitored, including input and output cards, amplifiers, power supplies, wiring, speaker coils, activation devices and appliances, as well as intercom and call stations. Maintenance reports should be self-generating to ensure that repairs are made in a timely fashion. These reports should be automatically directed to emergency services personnel, to the maintenance department, or to the organization contracted to provide repair services. Logs should also be generated to show that failures have been repaired.
Design and clarity
System layout in a plant environment requires the experience of trained field technicians and engineers. In an existing plant, sound level surveys should be completed, and speaker placement determined. Many factors must be taken into account for speech messages to be heard and understood. First, the message should be broadcast at 10 to 15 dB above the ambient noise level. Speakers should be placed near noise sources, as the sound will attenuate at the same rate as the noise. The system should allow for varying output levels based on the ambient noise level. For example, during maintenance shutdowns it is desirable to reduce the overall output, as long as it remains 10 to 15 dB above ambient. It may also be desirable to reduce the output at night, to avoid having a negative effect on neighbours. Speakers must be of a similar type and placed in a way to limit or eliminate reverberation (echo). This ensures that the message will not be garbled. The presence of large structures such as buildings, vessels, and so on may create an acoustical shadow. Within the shadow, the message will be at a lower sound level, and may not be heard or understood. It can also happen that messages from different speaker arrays may arrive at a location at slightly different times. Depending on the time differential and the sound intensity, the message may be unintelligible. Weather effects such as wind speed, direction, temperature, and humidity levels can also have a negative influence on sound level quality and level.
The design and implementation of an Emergency Warning System or Mass Notification System requires a thoughtful process to determine what the potential emergencies are, and what should be done in the event that they occur. The system should be flexible and robust. It is important to work closely with the equipment manufacturer to ensure that the product will meet plant requirements now and in the future. The system should be designed in such a way that it can accommodate changes in its technology, changes within the plant environment, and changes in legislation. Such a system may not have the lowest price, but provides the best long term value, and ensures that emergency warnings are heard, understood, and acted upon in a way that preserves life, protects infrastructure, and the environment.
For more info, please contact: Paul Huene Accutech Industrial Systems; tel: 403 834 3414; email: firstname.lastname@example.org
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