Smoke alarms and dwelling unit systems: what NFPA 72 Chapter 29 requires
Every sleeping room, every level, all interconnected. Plus the power figure people quote wrongly and the replacement date people read from the wrong label.
Dwelling units are covered by their own chapter, NFPA 72 Chapter 29. It applies to single and multiple station alarms and to household fire alarm systems, and several of its figures differ from the rest of the Code in ways that catch people out.
Where smoke alarms go
Smoke alarms go in every sleeping room, outside each separate sleeping area, and on every level of the dwelling.
Where two or more smoke or heat alarms are installed in a dwelling unit, suite of rooms or similar area, they are arranged so that any one operating sounds all of them. Carbon monoxide alarms are interconnected among themselves the same way. Mechanically powered single station heat alarms are the exception.
From the field
A basement alarm that cannot wake somebody upstairs is the failure the interconnection rule exists to prevent.
Secondary power: system or alarm
| Equipment | Normal condition | Then |
|---|---|---|
| Household fire alarm system | 24 hours | 4 minutes of fire alarm, or 12 hours of carbon monoxide alarm |
| Single or multiple station alarm | 7 days | 4 minutes of alarm, or 12 continuous hours for a carbon monoxide alarm |
Twenty four hours is the system figure. Quoting it at a standalone smoke alarm is wrong by a factor of seven.
Monthly testing is required
Single and multiple station alarms and connected appliances are inspected and tested at least monthly. That is a requirement, not a suggestion. The occupant is deemed qualified to do it, provided they have the manufacturer's information, and the installing contractor is required to hand that information over in writing on completion.
Replacement runs from the date of manufacture
Smoke alarms do not stay in service longer than 10 years from the date of manufacture, unless the manufacturer says otherwise. Not from the install date, and not when they finally stop working. Any alarm that fails an operability test is replaced regardless of age.
- A carbon monoxide alarm is replaced on its end of life signal or the manufacturer's replacement date.
- A combination smoke and carbon monoxide alarm is replaced on its end of life signal or 10 years from manufacture, whichever comes first.
From the field
The manufacture date is stamped on the back of the alarm. Check that, not the install sticker.
Carbon monoxide alarms
Whether carbon monoxide detection is required at all comes from other codes. Once it is required, NFPA 72 Chapter 29 and NFPA 720 place the alarms:
- Outside each separate sleeping area, within 21 ft of any sleeping room door, measured along the path of travel.
- On every occupiable level, including basements but not attics or crawl spaces.
- In any sleeping or guest room that itself contains a fuel burning appliance.
A carbon monoxide condition is signalled distinctly from fire. The audible signal is the temporal four pattern, not the temporal three used for fire evacuation, and carbon monoxide alarms carry a minimum rating of 85 dBA at 10 ft. In residential occupancies, after the first 4 minutes of alarm the 5 second off period may stretch to 60 seconds.
From the field
Listen to the pattern rather than trusting the label on the panel. A carbon monoxide input programmed to sound temporal three is a real defect.
Keep reading
Pathway classes in plain English: Class A, B, C, D, E and X
The class tells you what a circuit does when something goes wrong with it. Here is each letter, and the field checks that catch a mislabelled one.
Class K extinguishers and the placard beside an automatic system
The portable and the hood system work as a pair, in a set order. The placard that says so is small, cheap and almost always missing.
Duct smoke detectors: what they are for and what they are not
A duct detector protects the air handler from spreading smoke. It does not protect the room, whatever the owner believes.