A 2:45 a.m. alarm on the seventh floor of a Pioneer Square high-rise emptied the building, and the water stayed behind

SEATTLE, Wash.

A residential high-rise in the 100 block of Second Avenue South in Pioneer Square was evacuated early on November 3 after an automatic alarm at 2:45 a.m. sent Seattle Fire Department units to a fire on the seventh floor, according to the department's incident logs as reported by MyNorthwest and the department's own Fireline record.

The fire itself was confined to a floor of the building. The operational consequence was water. Sprinkler discharge on an upper floor of a residential tower produces a volume that tenants rarely anticipate, and the runoff migrated down through the building's vertical penetrations rather than staying in the unit of origin. Residents were displaced while remediation work was carried out.

That sequence, a small fire and a large displacement, is the standard outcome of a sprinkler-protected high-rise fire. It is worth understanding precisely, because it determines what a building owner has to do in the days after the trucks leave.

What a 2:45 a.m. automatic alarm actually sets in motion

An automatic alarm from a high-rise fire alarm system is not a single signal. It arrives with an address: a floor, a zone, sometimes a device. The responding companies know before they arrive which stairwell to take and whether the alarm originated at a pull station, a smoke detector or a waterflow switch on the sprinkler system.

In a residential tower of this type the sequence typically runs through the building's fire command center. Elevators are recalled to the ground floor on Phase I, the lobby annunciator identifies the initiating device, and the standpipe system supplies the attack lines from a point below the fire floor. Crews connect on the floor below and work up, which keeps the hose out of the stairwell they may need for evacuation.

The timing matters for a different reason. Between 2:45 a.m. and the arrival of the first engine, the building's occupants were doing what a high-rise evacuation plan asks of them: leaving by the stairs in the dark, in whatever they were wearing, from the seventh floor and above. Most residential high-rise fire deaths in the United States occur in the unit of origin, and the occupants who leave early are usually the ones who were never in danger.

A sprinkler head is a small device with a large water bill

A single residential sprinkler head flowing at its design pressure discharges on the order of 15 to 25 gallons per minute. In ten minutes of operation that is between 150 and 250 gallons, delivered into a room at ceiling height, where it spreads across the floor and finds every opening in the slab.

In an apartment that means the unit below, and the unit below that. Water follows pipe penetrations, electrical chases, and the gap at the base of a drywall partition where the acoustic sealant has failed. It reaches the elevator pit, the electrical rooms on lower floors, and the parking garage ceiling. A fire that damaged one room can leave a dozen households out of their homes for weeks, and the remediation is the reason: saturated drywall, insulation and flooring have to come out, and the assemblies have to be dried and tested before the units can be reoccupied.

The alternative is worse. Buildings without sprinklers in the same configuration lose the floor and sometimes the tower. The water damage is the price of the system working.

When the system that worked becomes the system that is out

After a discharge, the affected sprinkler heads are replaced and the zone is restored, but a building can be left with a portion of its protection isolated for longer than the repairs suggest. Piping damaged by heat, valves closed during investigation and left closed, and control valves that no one returns to the open position are the ordinary reasons a system sits impaired after a fire.

NFPA 25 sets out the inspection, testing and maintenance regime that governs the restoration, including the impairment procedures that apply when a system or zone is taken out of service. Where the impairment extends beyond the period allowed by the code and the authority having jurisdiction, a fire watch is required for the affected areas. In a high-rise that is a floor-by-floor assignment, not a lobby post.

There is a second impairment that gets less attention. Alarm systems damaged by water in a riser room or a lower-floor electrical space can leave the building without detection while the suppression system is back in service. A building with sprinklers and no alarm is a building where a fire on an upper floor is discovered by a neighbour rather than by the system.

The residents carry the dislocation

Displacement in a high-rise is not measured by the units the fire touched. It is measured by the units the building official will not release, which is a function of water, electrical safety and elevator service. Residents on unaffected floors often return the same day. Residents below the fire floor sometimes wait weeks for ceilings, wiring and floors.

For the owner, the practical work in that window is access control and supervision of a building full of contractors with the doors propped. Service corridors and stairwells that are normally locked are open all day. For a property manager, the exposure after a high-rise fire is unauthorized entry into vacant units and theft of salvageable property.

Elevators, stairs and the people who cannot take them

The defining feature of a high-rise fire is vertical distance. In a seven-story building the fire floor is reachable by stair, and the evacuation is a walk down a protected shaft that most occupants have never used before. In a building of twenty floors or more the same walk is a physical event for anyone with a mobility limitation, and the elevator recall that protects riders from a fire floor removes the only alternative they had.

That is why high-rise evacuation planning in residential buildings relies on defend-in-place for occupants away from the fire floor, and why the alarms in those buildings are zoned rather than general. The people who must leave are the ones on and near the fire floor. The people who must stay put are the ones for whom a stairwell in smoke is a greater risk than a closed apartment door.

The Seattle incident followed that pattern at 2:45 a.m., with residents leaving in the dark and the fire confined to one floor. The operational question afterwards is whether the stairwells stayed clear, because a stair that fills with smoke from an open apartment door is a stair that cannot be used for anything.

Drying a building is an engineering job

Water that leaves a sprinklered apartment has already been classified by the restoration industry. Clean water from a domestic supply becomes contaminated as soon as it crosses a floor assembly, and the material it passes through decides what can be dried in place and what has to be removed.

Drywall that has been wet for more than a day or two is generally cut out rather than dried, because the paper facing supports mould growth in a closed cavity. Insulation loses its value once saturated and does not recover. Engineered floor systems, which are common in newer residential construction, are particularly unforgiving: the oriented strand board web is not designed to stay wet, and a floor that is dried slowly can lose capacity even after it looks sound.

The restoration sequence therefore runs from extraction to controlled demolition, then to drying with air movers and dehumidifiers, then to verification with moisture meters and thermal imaging, and only then to rebuild. Building officials and insurers generally want that sequence documented, and the documentation is also what allows a building to be reoccupied floor by floor instead of all at once.

What the building owes its tenants while it is half closed

A residential tower under remediation is a building with several simultaneous conditions. Service corridors are full of contractors. Doors that are normally locked are propped. The alarm system may be partially disabled in the areas being worked, and the sprinkler system may be isolated in a zone that was drained.

That combination has a code consequence. Where suppression or detection is out of service beyond the permitted interval, the impairment procedures of NFPA 25 and the local fire code apply, and a fire watch is required for the affected areas. In a tower, coverage is assigned by floor and by system zone rather than to a single point at the entrance.

The practical consequence is about who is in the building. Tenants returning to unaffected floors, contractors working above and below them, and vacant units awaiting repair all share the same corridors, and the post that controls access is also the only presence on site overnight.

The USPA position

USPA Nationwide Security provides fire watch coverage in Seattle for buildings with impaired suppression, alarm or standpipe systems, and uniformed officers for access control in occupied buildings under repair. Coverage can be opened through the emergency fire watch desk, and the scope a post should actually cover is described in the fire watch white paper.

Related reporting from the newsroom: One person was hospitalized after a late-night fire at Connor Tower in Johnstown, Pennsylvania, and a woman was critically injured falling from a window during a three-alarm fire at Cooper River Apartments in Pennsauken.