Douglas Krantz - Technical Writer - Describing How It Works
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Why are there Two Fire Strobes in some Apartment Bedrooms?

A handicap apartment has two fire alarm systems, the individual system using smoke alarms with strobes, and the common area fire alarm systems horns and strobes
The common area fire alarm system horn and strobe in a handicap (ADA) apartment has to sound as loud and flash as brightly as the handicap (ADA) smoke alarm w/strobe. The two systems, though, aren't compatible with each other.


By Douglas Krantz

Separate Systems - Same Requirements

Multifamily dwellings like apartments, condominiums, hotel rooms, etc., actually have two fire alarm systems: each individual residence's fire alarm system and the building's common fire alarm system.

A fire alarm system, any fire alarm system, detects fire and warns people of fire. Greater requirements by the ADA (Americans with Disabilities Act) do not change the idea of detection or the idea of warning people; the detection is still there, and the warning is also there, but enhanced. The ADA's required warning enhancements, though, only mean more and higher intensity strobes along with louder and sometimes different sounding warning devices.

Besides detecting fire in any dwelling that has two fire alarm systems, both of the systems must be able to warn the residents of the fire. When installing two systems, three areas of concern are important: How reliable are the two systems? How compatible are the two systems? How serviceable are the two systems going to be for years to come?

Each Individual Dwelling Fire Alarm System

The residential smoke detector/sounder system is a system of stand-alone smoke alarms. Keep in mind that the smoke alarms in each residence have to be wired together so when one sounds off, all of the smoke alarms in that dwelling sound off.

In that dwelling, when there's smoke, the smoke alarms warn the residents there might be a fire and to get out, or if it wasn't a real fire, the smoke alarms warn the residents to turn off the stove. Basically, the smoke alarms get the resident's attention, but if the alarm is caused by cooking smoke, this stand-alone system doesn't have to get everyone else out and into the parking lot.

Whether it's a normal dwelling or a handicap (ADA) dwelling, the smoke alarms detect smoke in the dwelling unit.

Common Area Fire Alarm System

For the whole building, there's a common area fire alarm system. The common area fire alarm system covers not just the halls and lobbies, but because the sprinkler system for the whole building is included, all the residences are included in the detection. That means the dwellings are part of the common area fire alarm system.

Whether it's in a residence or in a hallway somewhere, if it's a real fire, the heat of the fire will open a sprinkler head so it sprays water. When this happens, water starts flowing and the common area fire alarm system warns everyone else in the building to get out.

ADA Fire Alarm Warning Systems

Both fire alarm systems have to warn the residents of fire, so both systems are required to have the same brightness and sound level for the warning strobes and horns. Basically, unless both systems are combined some way, there has to be parallel warning systems; both systems require strobes (in a handicap or ADA unit) and both systems require sounders.

Combined Warning Systems (Compatibility)

Physically separate systems, like AC utility powered smoke alarms next to DC 24 volt common area fire alarm NAC (Notification Appliance Circuit) horns and strobes are not electrically compatible; they don't work together without extra parts and design work.

Yes, relays can be installed so the building's common fire alarm system can be used to activate the strobes and sounders on the handicapped (ADA) unit's smoke alarms, but there are two issues that prevent that from normally being done.
  1. To make sure both systems are reliable and work when a fire occurs, both systems are required to be listed for use by some testing laboratory like UL, FM, or CE. Combined systems like AC utility powered smoke alarms and 24 volt NAC circuits aren't usually listed for fire alarm use.

  2. The combined systems will eventually break down. To make sure the system will be serviced properly for the next 20 years, all future technicians will require proper as-built (blueprint) diagrams on site.

    There's a problem that the service technician has to deal with though, proper as-builts are not normally available.

Reliability - Compatibility - Serviceability

To have a reliable warning system (horns and strobes), both the individual smoke alarm system and the common area fire alarm system should be completely separate and not connected together. The bottom line is that any room that has an ADA required strobe and sounder (smoke alarm with strobe) needs a second minihorn and strobe that is powered by the common area fire alarm system.
Based on his electronics training, and his understanding of Life Safety, Douglas Krantz has compiled his knowledge of Conventional Fire Alarm Systems into the book Make It Work - Conventional Fire Alarms. The book covers the basics of the Conventional Fire Alarm System, and shows how Life Safety and internal supervision affects the fire alarm system.

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

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