Survival Strategies for Fire Alarms Systems
October 01, 2002
Appeared in Building Operating Management/FacilitiesNet
Since Sept. 11, there has been new concern among building owners and occupants about the survivability of fire alarm systems — their ability to remain functional even under the most adverse conditions. The events of that day have increased fire safety awareness throughout the country and underlined the need for reliable fire alarm and communication systems in commercial buildings.
A number of factors contribute to the survivability of the fire alarm system. The most important is system architecture, which should be dispersed throughout the building. For example, in older systems, a single data-gathering panel and amplifier were usually placed in one location, so if an incident occurred adjacent to this location to disable the panel, the entire system would fail.
Today, the panels are distributed over many different areas, often on every third or fourth floor, and are able to operate alone. They will continue to function even if there is a failure at the head end or in the communication network. The audio system components are also designed with built-in redundancy and distributed throughout the building, so communication will carry on even if one or more of the amplifiers goes down.
Upgrades in head-end equipment — the fire alarm control panel and the fire command station — have also improved survivability. In older systems, the control panel was usually hidden out of sight, typically in a non-conditioned and unsupervised area, such as the basement, and had no associated audio system. Contemporary panels are not only equipped with voice communication capability but are also more effective when positioned on the ground floor.
The fire command station is also sited in a prominent position — the main building lobby. This is a modification applauded by fire departments and engineers, yet less appealing to architects. Local building codes determine the specific locations of both the control panels and fire command station required by the authority having jurisdiction.
Auxiliary Command Station
Within the past five years, it has also become common to institute an auxiliary fire command station at a second site in the building. This station is an exact replica of the first, with a full set of controls, but is separated from the primary station by at least a two-hour fire-rated construction element — that is, beyond one or more firewalls designed to keep systems from being exposed to fire and to provide additional response and evacuation time.
Each station is separately manned. The two do not operate simultaneously to avoid issuing conflicting instructions. All new safety systems include provisions for remote command stations, subject to the approval of local authorities. They do increase costs so the owner must decide whether to have these systems specified and installed. Nonetheless, recent events appear to have encouraged owners to include auxiliary stations as an additional level of protection to facilitate system survivability, occupant safety and evacuation.
Continuous communication is critical for fire safety, so upgraded communications risers go hand in hand with improved system architecture. Network communications are now designed with protocols that do not depend on a single pair of wires from panel to panel. Instead, the communications path is wired in a loop from the last panel on the riser back to the head end, enhancing network communication survivability. This circular path allows for unimpaired two-way communications even if part of the path is knocked out. Each system should include both a primary and a redundant fire-protected riser installed at a distance from each other and separated by at least one two-hour rated construction.
A suitable power supply is essential to the survivability of the fire alarm system. The fire safety system should be hardwired to a dedicated power source and circuit that are not utilized for any other equipment in the building. That eliminates the chance for other equipment or system malfunctions to jeopardize the primary power source, leaving the safety system inoperable.
There should be a secondary source for emergency power. This backup power source, an emergency life-safety generator, for example, is sometimes mandated by local code for such building types as high-rise commercial structures and health care facilities. International code requires the generator for new construction. Because the secondary power supply is cost-intensive, the owners of other types of buildings must make their choice on the basis of costs and benefits.
It might also be prudent to install a tertiary source, such as batteries placed in proximity to fire alarm panels. An additional option is an uninterruptible power supply system. These systems will maintain power for only a limited period of time, but they furnish a window for immediate emergency action. Although it will be costly to have four distinct power sources and that approach may not be seen as a necessity in most cases, each adds a level of survivability to the system and ensures a greater degree of safety.
There are also several choices in the types of wiring used for the installation of field devices, such as smoke detectors, speaker strobe lights and sprinklers. Class A wiring is composed of a primary circuit with a return that will ensure the device’s operability even if there is a break in the wire. This method, however, is very expensive because it doubles the amount of fire alarm cable required and increases the associated labor cost. Class B wiring provides for just a single pair of wires to every device with no return circuit and does not ensure full system survivability. The modern systems are also fully supervised as required by codes and standards. As a result, the use of Class B field circuits, as approved by NFPA 72, are common in today’s installations.
Furthermore, rather than connecting all the devices to a single circuit, each floor should include multiple addressable initiating circuits and multiple notification circuits. Although a single circuit may have the rated capacity to handle all the devices on a given floor, it is preferable to distribute the devices so they are not all dependent on one circuit. Another device that many building owners are currently investing in is a firefighter telephone system to enable two-way communication from all locations in the building to the fire alarm control panel. This type of system was only previously used in high-rise applications.
The specific sequence of operations is also important to survivable systems. The fire alarm system should be linked with the other critical building systems — elevators, HVAC and fire pumps, for example — to control them in the event of an emergency. The alarm system should be laid out in such a way that it will interface with the control mechanisms of these systems and its activation will shut them down or start them up as required.
Finally, there is the human element, the most important factor of life safety. Thorough training of end-users is necessary to ensure that the systems will achieve their aims. Even the most sophisticated and survivable systems will not suffice if fire safety personnel and building occupants do not know how to respond correctly to an alarm. A thorough evacuation plan and fire safety training must be initiated in all buildings to take full advantage of the safety systems and features built into the building.
Owners Must Make Choices
Although many of these features have not yet made their way into building code requirements, they are all desirable to enhance protection against unforeseen events. The installation of new features is not restricted to new construction; they can all be added in retrofits. Because the newest systems have an impact on the available space, the owner must decide whether to give up the real estate required for redundant risers, distributed panels and backup power sources and must select the systems most appropriate to the property.
In new construction, the increase in equipment and materials required by the redundant elements will increase construction time, which will affect scheduling. It should also be understood that retrofitting an occupied building will cause disruptions to the active working area. In both cases, it is evident that upgrading fire-safety systems does lead to added costs that bring no obvious return on investment.
Building owners tend to seek the most cost-effective and code-compliant systems installation and may hesitate to upgrade unless local law or their insurance underwriter requires them to do so because of a specific hazard or threat. Yet it is no less evident, especially since Sept. 11, that increasing the safety of occupants has benefits of its own.
James Carrigan is a senior engineer for fire and life safety in the New York City office of Syska Hennessy Group, a national consulting, engineering, technology and construction firm.
He is also a chief officer and firefighter/paramedic with the East Rockaway (N.Y.) Fire Department, which was actively involved at Ground Zero on Sept. 11, 2001.