Is there a difference between a smoke detector (SD) and a smoke alarm (SA)? Yes, there is, and we are partially directed by the applicable building and/or fire code where we are to use each type. But if you care and understand what the short and long-term savings can be by choosing the correct one, then I suggest you continue reading.
A smoke detector is a low-voltage, smoke-sensing device and is connected, powered and monitored by a fire alarm control unit (FACU). It is usually found in common spaces in apartment buildings, condominiums and hotels/motels as well in any premises where smoke detection is required by code or desired by the property owner or others. The fire alarm (FA) system designer will place these detectors in areas per a National Fire Protection Association (NFPA) standard, and will be programmed to evacuate a section of a building or the entire building. If properly installed in an area acceptable to the type of smoke detector being used, and if it’s maintained and cleaned regularly, a smoke detector will provide acceptable service for many years. There are smoke detectors currently in use that were installed more than fifty years ago. Smoke detectors are installed using FPL type of low-voltage wiring. Smoke detectors are required by an NFPA Standard to be tested annually.
A smoke alarm is usually a line voltage smoke-sensing device. Line voltage means 120 volts alternating current (VAC), the common voltage used in residential and other occupancies. There are battery-operated SAs available but they have limitations in their use. Per an NFPA Standard, the testing frequency shall be as recommended by the SA’s manufacturer to ensure their designed operation when needed, usually monthly. They are not connected to a monitoring unit like the smoke detectors and therefore the more frequent testing requirement. SA’s also have a stand-by battery to operate the device for 12 hours should the 120VAC power fail. The electrical wiring must be acceptable by the national electrical code (NEC) ,120VAC, 15 -20 ampere circuit wiring
Both types of detectors use either photo-electric or ionization type detection. Both sense smoke, but ionization will detect some of the invisible products of combustion. It’s important for the FA system designer to know what flammable materials or liquids will be in the area where smoke detection is to be installed so that they can make the proper decision on the type of detector to be utilized.
SA Applications:
Occupancy
Households
Hotels/Apartment
Houses (R1)(R2)
Required
SA’s or SD’s
SA’s and SD’s or all SD’s
Notes
One & two family
Three units or more
The rest of this presentation is directed at the following individuals:
Architects
Electrical Engineers
Developers
Maintenance Supervisors
Electrical Contractors
Property Owners
Fire Alarm System Installers
Where smoke detection is required in one and two-family households as well as hotels and apartment houses in excess of two units, smoke alarms can almost always be replaced with smoke detectors during the design phase. There are a few cost advantages of which you should be aware. The costs to be considered here are testing of the devices, battery replacement, device replacement and installation.
Testing:
1. The SAs, as required by code, are to be tested monthly. The writer is not an attorney, but if an agreement is not made with the tenant or others and the devices are not tested, what is the limitation of your liability? The code states that the owner has the responsibility for any system or device malfunction.
2. Utilizing SDs in place of SAs will eliminate the monthly testing as the FACU will monitor the SDs. Maintenance/labor cost reduction with the use of SDs.
Battery Replacement:
1. If the SA back-up battery is NiCad or carbon/zinc, it needs to be replaced annually, which can be done when the testing occurs or at least annually. The newer models have Lithium-Ion batteries and the entire SA will need to be replaced every 10 years, as required by code.
2. As the SDs are connected to an FACU, the FACU has a back-up battery system which has an anticipated life span of four years. Note reduced maintenance labor and battery cost when using SDs.
Device Reconfiguration:
1. Using SAs, a sounder or sounders will be required within each living unit to alert the occupants when the building fire alarm systems is in alarm as a SA is not connected to the building’s FACU
2. Using SDs with sounder bases, the sounder base will operate as a SA within the living unit, and not throughout the building. In addition, that same sounder base can be used when the building alarm system is in alarm, and therefore no additional sounding appliance is required. Construction equipment and labor costs are reduced. (When the building FA alarm system is a voice evacuation system, adequate speakers will then be required within the living unit. The local SD with sounder base will still replace the SA, but the building alarm system will use the speakers for instructions and evacuation)
3. In units for the hearing-impaired, the required high intensity visual appliances, or strobes, can be programmed to operate locally for a local alarm and all sounder bases to operate in all units, or a zone of units, as well as the common areas during a building FA system alarm.
Other Advantages:
The use of SDs also allows the monitoring of the alarm conditions in the living units at a central location, and the event is date/time stamped and stored in memory at the FACU. This can be helpful particularly in hotel/motels as well as in 24/7 staffed apartment complexes, especially if it occurs frequently.
The connecting wiring, and therefore the power, is supervised when using SDs. In addition, a message will be sent to the FACU that the detector is missing should it be removed from its base.
Expense:
The following is a recap of the differences in the cost of using SAs vs SDs. These are generalizations, but a FA designer with a FA installer could estimate the cost difference for your project(s)
SA Battery Cost
Replacement labor
Testing labor
Wiring cost
Equipment cost
Installation labor
Detector Replacement
SA
Yes
Yes
Monthly
Equal
Less
More
10 Years
SD
None
None
Annual
Equal
More
Less
Est. 25 Years
The equipment cost for using SDs will, of course, depend upon the owner/developer’s plans for the property. For short term ownership, on strictly a cost basis, SAs would be the most cost-effective path. From the writer’s experience, the added initial cost for SDs has an ROI of approximately 3-5 years. This does not include the cost that would be encountered in 10 years for the replacement of the SA’s. All of this will, of course, depend on several factors including labor, the cost of materials, etc.
In conclusion:
For new or rehabs in R1 and R2 projects where you wish to look into using SDs in place of SAs, use a FA system designer who is familiar with the method presented herein. As always, it’s best to contact the building department and/or fire alarm person (AHJ) who will be reviewing the plans for permitting. Contacting this person or persons is a good practice for all systems to ensure the designer is providing for all that is required in the local jurisdiction. A discussion concerning the replacement of SAs with SDs with the AHJ(s) is recommended, and at the same time, the code requirements for the jurisdiction can be discussed if that information is not available on the internet. You will find that some AHJs are not familiar with the replacement process, and their response might be that they will review the submitted documents and save their comments for them.
If you have any questions or comments, please contact Robert Hill & Associates LLC.
Bob Hill
Robert Hill & Associates LLC
Fire Alarm System Design Assistance
(866) 388-0023
