Max number of wireless smoke detectors in a multi-family

[veerasam]

Quoting from a related (closed) thread on this website, "Had time so I found a copy of NFPA 72 2010 edition handbook. 29.8.2.2 which has the requirement of 18 initiating devices 12 of them smoke detectors if the system is not supervised. If the system is supervised you can have 64 devices w/42 being smoke detectors. In the handbook intent was for unsupervised systems there was no way to monitor the integrity of the interconnecting wiring so was limited to smaller systems"

If monitoring the integrity of the interconnecting wiring was the reason for the limit, why does the same limit apply to wireless devices?

My current need: A four-plex building (basement + 2 floors) needs 2 detectors in basement plus one in each floor plus 5 (one in each bed for 3-bedrooms plus two in common area) in each residential unit for a total of 24 detectors.

Any suggestions on how to solve for the current need?
Sam

 

[kwired]

Quoting from a related (closed) thread on this website, "Had time so I found a copy of NFPA 72 2010 edition handbook. 29.8.2.2 which has the requirement of 18 initiating devices 12 of them smoke detectors if the system is not supervised. If the system is supervised you can have 64 devices w/42 being smoke detectors. In the handbook intent was for unsupervised systems there was no way to monitor the integrity of the interconnecting wiring so was limited to smaller systems"

If monitoring the integrity of the interconnecting wiring was the reason for the limit, why does the same limit apply to wireless devices?

My current need: A four-plex building (basement + 2 floors) needs 2 detectors in basement plus one in each floor plus 5 (one in each bed for 3-bedrooms plus two in common area) in each residential unit for a total of 24 detectors.

Any suggestions on how to solve for the current need?
Sam

Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

 

[veerasam]

Interconnection between occupancies

Interconnection between occupancies

Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

Yes. The inspector asked "If a fire starts in a basement the how will the occupants know to get out?"
I presume, he will also ask "If the fire starts in a first floor unit, how will a second floor unit occupant know to get out?"

 

[veerasam]

Interconnection between occupancies

Interconnection between occupancies

Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

Yes. The inspector asked "If a fire starts in a basement. how will the occupants on first floor know to get out?"
I presume he will also ask "If a fire starts in the first floor unit, how will the second floor unit occupant know to get out?"

 

[gadfly56]

Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

This is forbidden by code. You can't have toast burning in Unit A setting off alarms in Unit B.

 

[kwired]

This is forbidden by code. You can't have toast burning in Unit A setting off alarms in Unit B.

I kind of suspected that to be the case. Also expect there normally would be at least 1 hour finish between units required as well, maybe even 2 hour finish in some instances.

 

[gadfly56]

I kind of suspected that to be the case. Also expect there normally would be at least 1 hour finish between units required as well, maybe even 2 hour finish in some instances.

The exception would be if you had a building-wide FACP covering the common areas and pull stations or water flow switches. Then you can put a notification appliance inside each unit that tells everyone to get out of Dodge. However, you're still not tripping on an alarm device in any dwelling unit.

 

[veerasam]

The exception would be if you had a building-wide FACP covering the common areas and pull stations or water flow switches. Then you can put a notification appliance inside each unit that tells everyone to get out of Dodge. However, you're still not tripping on an alarm device in any dwelling unit.

Just to clarify the context: It is a 1920's building in original structure. No sprinklers. The building was re-plumbed and rewired in 2010 when they ran wiring for interconnected smokes. No one lives in basement (it has only a laundry area, electric water heaters and storage). Two floors are above basement. Each floor has two residential units (one on left half and one on right half of the floor).

 

[veerasam]

Do you need interconnection between occupancies? Might depend on structural rating between occupancies.

Yes. The inspector asked "If a fire starts in a basement. how will the occupants on first floor know to get out?"
I presume he will also ask "If a fire starts in the first floor unit, how will the second floor unit occupant know to get out?"

 

[K8MHZ]

I did a similar set up several years back. Here is how we set things up, and the inspector liked it.

We used wireless alarms. Each apartment was set up with it's own digital ID. In the basement, (common area) we installed four alarms a few inches from each other, one for each apartment system. That way, an alarm in an apartment wouldn't set off the alarm in another apartment, but smoke in the common area would set off all of them.

I think there are better wireless links now that would allow for a single multi channel unit in a common area.

 

[dhalleron]

We used wireless alarms. Each apartment was set up with it's own digital ID. In the basement, (common area) we installed four alarms a few inches from each other, one for each apartment system. That way, an alarm in an apartment wouldn't set off the alarm in another apartment, but smoke in the common area would set off all of them.

If I were going to do this without a fire alarm system, this makes the most sense to me. I would not want one apartment setting off the alarm in another apartment. A few times burning toast and the fire department showing up because someone called and the fines will start piling up.

 

[gadfly56]

Just to clarify the context: It is a 1920's building in original structure. No sprinklers. The building was re-plumbed and rewired in 2010 when they ran wiring for interconnected smokes. No one lives in basement (it has only a laundry area, electric water heaters and storage). Two floors are above basement. Each floor has two residential units (one on left half and one on right half of the floor).

The plot thickens. The original prohibition on putting all the dwelling units on the same smoke alarm circuit had two foundations. One was in section 11 of NFPA 72-2007. The other was the prohibition in the NEC on running a circuit between two dwelling units. In the 2010 edition of NFPA 72 that prohibition disappeared, but the NEC still wouldn't let you run wire from domicile A to domicile B. No one apparently considered wireless smoke alarms in all this. So, technically there's no current prohibition that I'm aware of for wireless smoke alarms. However, they went into some detail now on the hookup between the dwelling unit smoke alarms and a premises fire alarm which says that in that case, the dwelling unit sends a supervisory signal to the FACP and does not cause a general alarm.