Safety: Do You Need An MNS?

Regulations may not require a mass notification system but it still may be a good idea.

By Jim Otte, SSOE Group

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This is a huge financial advantage, particularly in a business that operates on small margins. The cost to shut down and restart equipment added to the lost productivity due to a full-scale evacuation can mean a loss of hundreds of thousands of dollars.

A company can further improve the effectiveness of its mass notification efforts by adding voice messaging to a zonal system. This enables communicating information about the emergency situation and providing essential directions on how employees must respond. For example, in the case of a chemical vapor cloud, occupants must know what direction the wind is blowing and where they must go to avoid the advancing vapors. In case of a fire or chemical spill, specific evacuation instructions can be broadcast to warn occupants of the particular areas of the building that are hazardous.

Voice messaging is clearly the preferred system if several important qualifications are met: it must be concise, audible throughout the facility, and intelligible. Intelligibility standards adopted by the ICC and NFPA take into account such attributes as speech and background noise levels, as well as reflections and reverberations from walls, floors or other structures.

Of the national regulatory agencies that could mandate MNSs during construction at chemical facilities, only OSHA is requiring some sites to provide an MNS. Currently, it narrowly focuses on alerting workers at new construction sites to potentially dangerous situations. For example, a high velocity windstorm can be a hazard for crews working on the upper floors of a steel substructure. In most cases, construction sites aren't set up for standard MNSs; therefore it becomes the contractor's responsibility to provide another means of alerting workers — e.g., via two-way radios, pagers, etc., which, of course, are only short-term solutions.

Unfortunately, these requirements aren't documented for contractors to reference. Rather, the need may be noted when OSHA conducts an inspection of the construction site. Factors such as the number of workers and the size of the project impact the inspector's decision to require a site-wide communication system. It's not unusual for OSHA to give the general contractor a week or two to comply. This makes a strong case for investing in the installation of a communication system before construction starts. Ultimately, the responsibility for mass notification falls to the chemical plant owner because it's responsible for costs and schedule.

Chemical companies are increasingly relying on radio systems, textual signs and notification of the neighboring communities.

Some plants require certain staff members to carry a radio at all times. It not only serves as a means to communicate with other personnel on a daily basis but also receives a prerecorded alert message or live instructions on what to do in the case of an emergency. A person receiving an alert message is responsible for relaying this information to people not carrying a radio, typically vendor and contract staff.

Textual signs can do more than convey alert messages. At other times, they can provide information such as the time and date, weather conditions, announcements of company activities or the employee of the month. The objective is to get all people on site to look at the sign every time they pass it and rely on it to give them information.

Notifying neighboring communities if a scenario has the potential to be catastrophic poses two challenges: keeping alerts that are for internal purposes only within the fence line, and communicating effectively with those outside the perimeter when needed. A high-power speaker array system, if designed correctly, can accomplish both. A plant using radios for internal alerts would have to undertake additional tasks to notify surrounding areas. One approach is to go to each residence or building to convey the alert in person. Another involves installing a system using phone lines to auto-dial preprogrammed phone numbers and deliver a prerecorded message. Either way is cumbersome and not the most effective for delivering an emergency message.

The majority of chemical plants aren't required to install and maintain an MNS. However, it still may make sense to put in one. To assist in deciding, a professional designer/engineer should conduct a risk analysis. This involves evaluating a number of key items, including but not limited to: types of emergency events possible at the location, impacts to life, cost of evacuating or not evacuating, full versus partial evacuation, costs to restart operations, severity of the event, and impact on the site. Such an analysis will clarify the risk a facility is taking by not having an MNS as well as the respective costs of putting in and maintaining such a system.


JIM OTTE is a senior communications designer at SSOE Group, Toledo, Ohio. E-mail him at

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