How long can a fire alarm be down before a fire watch is required?

More than 4 hours out of service in a 24-hour period is the point at which NFPA 72 expects the authority having jurisdiction to be notified, and a fire watch or evacuation of the affected area is the usual requirement. Separately, IFC 901.7 requires you to notify the fire department and fire code official as soon as a required system goes out of service, regardless of how long you expect the outage to last.

Is the sprinkler threshold the same 4 hours?

No, and conflating the two is an easy mistake to make — several of the pages ranking for this question quote a single figure for both. NFPA 25 chapter 15 sets the trigger for water-based systems — sprinklers, standpipes — at more than 10 cumulative hours of impairment in a 24-hour period. Cumulative is the operative word: separate outages in the same day add together.

Can my existing security guard just do the fire watch?

Only if the fire watch is their sole assigned duty for that shift. A fire watch means patrolling the affected areas on a set route and interval, watching for fire, and nothing else. An officer who is also staffing the lobby, running access control, or monitoring cameras is not performing a fire watch, and an inspector will treat it as one not being performed.

Who decides how often the fire watch has to patrol?

Your authority having jurisdiction — normally the local fire code official. The model codes require the watch and require it to be approved, but the specific patrol interval is commonly set locally. Call and ask rather than picking an interval yourself; getting it in writing from them is also your best documentation.

Does a fire watch have to keep a written log?

Yes, in practice always. The log records each patrol with times and the watcher's name, kept as the patrols happen rather than reconstructed afterward. It is the evidence the watch was performed, it is what an inspector asks for, and after any incident it is the first document anyone requests.

When is a fire watch required?

If a required fire protection system in your building goes out of service, the model fire code says to notify the fire department and the fire code official immediately, and to either evacuate the building or post an approved fire watch until the system is back. The hour thresholds that force the issue are different for different systems, and that difference is easy to miss: for a fire alarm system it is more than 4 hours out of service in a 24-hour period, and for a water-based system like sprinklers it is more than 10 cumulative hours in a 24-hour period. Your local authority having jurisdiction can be stricter, and the edition of the code your jurisdiction has adopted is what actually binds you.

The two thresholds people mix up

Almost every page you will find on this subject quotes a single number — usually 4 hours — as if it covered everything. It does not. The 4-hour figure comes from the fire alarm side. Sprinklers and other water-based systems run on a different, longer clock, and it is cumulative rather than continuous.

Fire alarm system out of service — NFPA 72 treats more than 4 hours in a 24-hour period as the point where the authority having jurisdiction must be notified, and the usual answer is a fire watch or evacuation of the affected area.
Sprinklers, standpipes, and other water-based systems — NFPA 25 chapter 15 sets the trigger at more than 10 cumulative hours of impairment in a 24-hour period, at which point the building is evacuated or a fire watch is posted. Cumulative matters: three separate four-hour outages in one day is twelve hours, not four.
Either way, IFC section 901.7 requires immediate notification when a required system goes out of service, and gives the fire code official the authority to require evacuation or an approved fire watch until it is restored. Notification is not optional even when you are under the hour thresholds.

4 hours is the fire alarm number. 10 cumulative hours is the sprinkler number. If a vendor quotes you one figure for both, they are working from a blog post, not the code.

The other situations that call for a fire watch

System impairment is the common one, but it is not the only one. Fire watches also get ordered for hot work — welding, cutting, grinding, torch-applied roofing — where a watch stays on the area during the work and for a period after it stops. They get ordered during construction and renovation when the permanent fire protection is not yet in service, for some assembly occupancies and special events, and any time a fire code official simply determines the conditions warrant one. That last category is broad on purpose, and it is entirely at the official's discretion.

Who you have to call, and in what order

The fire department and the fire code official — immediately, not once the workday is over. This is the step buildings skip, and it is the one that turns a maintenance issue into a violation.
Your insurance carrier. NFPA 25's impairment procedures name the carrier explicitly for water-based systems, and most commercial policies have their own notice requirement with its own deadline.
Whoever is designated as the impairment coordinator. For water-based systems the standard expects the building owner to designate one person who owns the outage from start to restoration.
The alarm monitoring company, so a system in test or trouble is not being treated as a live signal — or worse, ignored when it becomes one.

For a sprinkler impairment, every affected valve also gets tagged so nobody downstream assumes the system is live. Tagging is cheap and it is the thing that gets noticed on inspection.

What a fire watch actually has to do

A fire watch is not a guard sitting at a desk. It is a person, or several, whose only assigned duty is walking the affected areas on a set route at a set interval, watching for fire, and having an immediate way to notify the fire department and alert occupants. No other duties. A guard who is also running the lobby desk or checking badges is not performing a fire watch, and an inspector will say so.

A written patrol route that covers every affected area, including the spaces nobody visits.
A set patrol interval. Your authority having jurisdiction may specify it; if they have not, ask them rather than choosing one yourself.
A log, kept contemporaneously, recording each patrol with times and the watcher's name. The log is the evidence the watch happened, and it is the first thing requested after an incident.
A reliable means of notifying the fire department immediately, and a way to alert occupants with the alarm system down.
Training on the specific building — where the exits are, where the standpipe connections are, what the hazards are.

How to hire one at 9pm on a Friday

Fire watch is an emergency purchase and it is priced like one. You are usually calling because an inspection just failed or a system just tripped offline, the building has to stay occupied, and the clock is already running. That is a terrible position from which to compare vendors, so compare a few things fast and take notes.

Can they start tonight, and how many officers can they actually put on site — not how many they have in the region.
Is it billed hourly per officer, with a minimum shift length, and what is the after-hours or holiday multiplier. Ask for the minimum in writing before anyone is dispatched.
Do they provide the log, and will you get copies daily. You will need them.
Are their officers licensed in your state, and are they covered by the company's general liability and workers' comp. Ask for a certificate of insurance naming your entity.
Have they done a fire watch in your building type before. A high-rise, a hospital, and a warehouse are not the same assignment.

Call your fire code official and ask what they expect for patrol interval and documentation. They would rather tell you at 9pm than write you up on Monday.

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Questions people ask next

How long can a fire alarm be down before a fire watch is required?: More than 4 hours out of service in a 24-hour period is the point at which NFPA 72 expects the authority having jurisdiction to be notified, and a fire watch or evacuation of the affected area is the usual requirement. Separately, IFC 901.7 requires you to notify the fire department and fire code official as soon as a required system goes out of service, regardless of how long you expect the outage to last.
Is the sprinkler threshold the same 4 hours?: No, and conflating the two is an easy mistake to make — several of the pages ranking for this question quote a single figure for both. NFPA 25 chapter 15 sets the trigger for water-based systems — sprinklers, standpipes — at more than 10 cumulative hours of impairment in a 24-hour period. Cumulative is the operative word: separate outages in the same day add together.
Can my existing security guard just do the fire watch?: Only if the fire watch is their sole assigned duty for that shift. A fire watch means patrolling the affected areas on a set route and interval, watching for fire, and nothing else. An officer who is also staffing the lobby, running access control, or monitoring cameras is not performing a fire watch, and an inspector will treat it as one not being performed.
Who decides how often the fire watch has to patrol?: Your authority having jurisdiction — normally the local fire code official. The model codes require the watch and require it to be approved, but the specific patrol interval is commonly set locally. Call and ask rather than picking an interval yourself; getting it in writing from them is also your best documentation.
Does a fire watch have to keep a written log?: Yes, in practice always. The log records each patrol with times and the watcher's name, kept as the patrols happen rather than reconstructed afterward. It is the evidence the watch was performed, it is what an inspector asks for, and after any incident it is the first document anyone requests.

Written for business owners by Most Recommended Security Guards, which measures which security guard companies AI assistants actually recommend in 8 U.S. metros. Nobody can pay to be on those lists. How we measure.