Sprinklers and fire alarm

Danielle Roy brings a sprinkler head to class, a small brass fitting with a glass bulb full of red liquid in its frame. She passes it round, then puts a second one in a clamp over a candle. After about a minute the liquid expands, the bulb shatters with a crack that makes Ingrid jump, and the small cap it was holding falls away. 'In a building, water would be coming out now,' Roy says, 'from this one head and no other. That is the first thing everyone gets wrong. In films the whole building goes off at once. In real life one or two heads open over the fire, and most fires in sprinklered buildings are controlled by the first two heads. That is why the code loves sprinklers. They are the most reliable life safety device we have ever invented.'

How sprinklers work

An automatic sprinkler system is a network of pipes filled with water under pressure, fed by a water supply and fitted with sprinkler heads at regular spacing across the ceilings. Each head is held closed by a heat-sensitive element, either a glass bulb filled with liquid or a fusible link of solder, that releases at a set temperature, typically about 155 °F for ordinary heads. When the hot gases of a fire reach a head, its element releases, water flows through the head onto a deflector that spreads it in an umbrella pattern, and the flow of water in the pipes trips a switch that sounds the fire alarm and calls the fire department. Heads farther from the fire stay closed. A sprinkler system is therefore both a fire suppression system and a fire detection system.

Sprinklers are old. Henry Parmelee patented an automatic sprinkler in 1874 to protect his piano factory, and Frederick Grinnell's improved heads spread through New England textile mills in the 1880s and 1890s, where insurers offered lower premiums to sprinklered mills. The National Fire Protection Association was founded in 1896 to standardize sprinkler installations, and its standard, NFPA 13, is still the basis of sprinkler design throughout North America. For most of the twentieth century sprinklers were installed mainly to protect property. Only in the last forty years have codes come to treat them as the central life safety system for most buildings, because the evidence of their effect on deaths is so strong: in buildings with working sprinklers, the death rate per fire is a small fraction of that in buildings without them.

Codes respond by requiring sprinklers in many buildings and by relaxing other requirements in buildings that have them. The International Building Code requires sprinklers, in Section 903, in every Group R occupancy, in Group A occupancies where a fire area exceeds 12,000 square feet or holds 300 or more people or is above the level of exit discharge, in Group E occupancies over 12,000 square feet, in Group I occupancies, in high-rise buildings and in many others. Its tables of allowable height and area give large increases for sprinklered buildings, travel distances are longer, exterior openings may be larger, and several fire-resistance requirements are reduced. In practice almost every new building of any size is sprinklered.

Kinds of systems

The most common system is a wet-pipe system, in which the pipes are always full of water. It is simple, reliable and fast. Where the pipes would freeze, as in unheated parking garages, loading docks, canopies and attics in a prairie winter, a dry-pipe system is used instead: the pipes are filled with compressed air or nitrogen, which holds a dry-pipe valve closed in a heated room. When a head opens, the air escapes, the valve opens and water fills the pipes. Dry systems are slower and need more maintenance, but they are essential in a cold climate. Preaction systems, which fill the pipes only when a separate detection system confirms a fire, protect spaces where accidental water damage would be costly, such as archives, computer rooms and museum storage. Deluge systems, with open heads that all discharge together, protect special hazards such as aircraft hangars.

Several standards are referenced for different buildings. NFPA 13 is the full standard for all occupancies, designed to protect both life and property. NFPA 13R is a lighter standard for residential buildings of up to four stories and 60 feet, designed mainly to protect life; it allows the omission of sprinklers from some spaces such as small closets, attics and concealed spaces, and buildings using it get no increase in allowable area. NFPA 13D is a simple standard for one- and two-family dwellings. The hub, as an assembly building, will be protected to NFPA 13. Greenway Homes could use NFPA 13R, but Danielle Roy recommends NFPA 13 throughout, partly for the attic space above the top floor and partly because the larger allowable area gives the design room to grow.

Designing a sprinkler system

Sprinkler systems are designed by fire protection engineers or specialized contractors, but architects must understand them well enough to plan for them. The design begins by classifying the hazard of each space, which depends on what will burn there and how fast. Offices, apartments, churches, libraries' reading rooms and most of the spaces in the students' projects are light hazard. Parking garages, laundries, restaurant service areas and mechanical rooms are ordinary hazard, group 1; library stack rooms, stages, dry cleaners and many shops are ordinary hazard, group 2; spaces with flammable liquids or high-piled storage are extra hazard or need special design.

For each hazard the standard sets a design density, the rate at which water must be discharged per unit of floor area, over a design area, the area of the most demanding part of the system that is assumed to be operating at once. For light hazard the density is 0.10 gallon per minute per square foot over 1,500 square feet, for ordinary hazard group 1 it is 0.15 and for group 2 it is 0.20, over the same area. Each head may cover up to about 225 square feet in light hazard spaces and about 130 square feet in ordinary hazard spaces. To the sprinkler demand the designer adds an allowance for the hoses firefighters will connect, 100 gallons per minute for light hazard and 250 for ordinary hazard, and the water supply must deliver the total for the duration the standard sets, 30 minutes for light hazard and 60 to 90 minutes for ordinary hazard.

# Rough sprinkler water demand for the hub (density/area method)
hazards = {  # space: (density gpm/ft2, design area ft2, hose allowance gpm, minutes, head coverage ft2)
    "library reading room (light)":   (0.1, 1500, 100, 30, 225),
    "library stacks (ordinary 2)":    (0.2, 1500, 250, 60, 130),
    "kitchen and storage (ordinary 1)": (0.15, 1500, 250, 60, 130),
}
for space, (dens, area, hose, mins, cover) in hazards.items():
    flow = dens * area                     # sprinkler flow gpm
    total = flow + hose
    heads = -(-area // cover)              # heads in the design area, rounded up
    volume = total * mins
    print(f"{space:<33} sprinklers {flow:6.0f} + hoses {hose:5.0f} = {total:6.0f} gpm for {mins} min "
          f"({volume:,.0f} gal), about {heads:.0f} heads operating")
floor = 16500                            # ground floor area of the hub (ft2)
print(f"heads to cover the ground floor at light-hazard spacing: about {floor / 225:.0f}")

library reading room (light)      sprinklers    150 + hoses   100 =    250 gpm for 30 min (7,500 gal), about 7 heads operating
library stacks (ordinary 2)       sprinklers    300 + hoses   250 =    550 gpm for 60 min (33,000 gal), about 12 heads operating
kitchen and storage (ordinary 1)  sprinklers    225 + hoses   250 =    475 gpm for 60 min (28,500 gal), about 12 heads operating
heads to cover the ground floor at light-hazard spacing: about 73

The library stacks set the demand: 550 gallons per minute for an hour, or 33,000 gallons of water. The city main on the avenue can probably deliver this without a pump, but the engineer will need a hydrant flow test to be sure. Callum learns two things for the plan. He needs a sprinkler riser room at the north wall near where the water service enters, about 10 by 10 feet, with its door to the outside or to a corridor, and he needs a fire department connection on the avenue face, within easy reach of a hydrant, where firefighters can pump water into the system.

Sprinklers also affect the architecture in less obvious ways. Heads must be spaced evenly and kept clear of obstructions such as beams, ducts and light fixtures, so exposed structure and coffered ceilings complicate the layout. Callum's exposed glulam beams in the wing, at 24 feet centers with CLT between, are deep enough that heads must be placed in every bay; the engineer will choose heads suitable for the obstructed construction. The hall's trusses, about 6 feet 6 inches deep, need heads at the level of the roof deck between them. Concealed heads with flat cover plates can disappear into a plaster ceiling, but every head, pipe and valve must still fit somewhere, and pipes cannot be buried in the CLT.

Standpipes and fire department connections

Standpipes are vertical pipes with hose connections in the exit stairs or near them on each floor, so that firefighters can connect their hoses inside the building without dragging them up from the street. The International Building Code requires Class I standpipes, designed to NFPA 14, where the floor of the highest story is more than 30 feet above the lowest level of fire department vehicle access, in many large assembly buildings and in other cases set out in Section 905. In most sprinklered buildings the standpipe and sprinkler systems share the same risers. Greenway Homes, whose top floor is about 31 feet above the street, needs hose connections in each exit stair.

Fire alarm and detection

A fire alarm system detects fire and warns the occupants. The International Building Code, in Section 907, requires fire alarm systems in many occupancies: in Group A where the occupant load is 300 or more, in Group E where it is 50 or more, in Group R-2 buildings where any dwelling unit is three or more stories above the lowest level of exit discharge or there are more than 16 dwelling units, and in many others. The system must be installed to NFPA 72. It includes a control unit, an annunciator at the main entrance or in a fire command center that tells firefighters where the alarm came from, manual fire alarm boxes at exits where required, smoke detectors in some spaces, the waterflow switches of the sprinkler system, and audible and visible notification appliances, the familiar horns and strobes, throughout. Large assembly spaces and high-rise buildings need voice alarm systems that can give spoken instructions. Each dwelling unit also needs its own smoke alarms, interconnected within the unit, and carbon monoxide alarms where there are fuel-burning appliances or an attached garage.

Roy explains why alarms are as much about people as about detection. People ignore alarms. They assume a false alarm, they finish what they are doing, they go back for belongings, they wait to see what others do. Studies of evacuations have found that the time people take to start moving is often longer than the time they take to walk out. Voice messages that say clearly what is happening and where to go get people moving faster than bells. Visible strobes reach people who are deaf or hard of hearing, and in sleeping rooms they must be bright enough to wake them. Frequent false alarms, from badly placed smoke detectors over toasters or in dusty rooms, teach people to ignore the real one; good design places detectors where they will not be set off by ordinary life.

Firefighter access and other systems

A sprinkler system and an alarm are useless if the fire department cannot reach the building. The International Fire Code requires fire apparatus access roads at least 20 feet wide, with 13 feet 6 inches of clear height, extending to within 150 feet of all portions of the building's exterior walls, with turnarounds for dead ends longer than 150 feet. Key boxes give firefighters access to locked buildings. Elevators must have firefighters' emergency operation, recalling them to the ground floor when the alarm sounds. High-rise buildings, with occupied floors more than 75 feet above the lowest level of fire department vehicle access, need smoke control, emergency power, fire service access elevators and a fire command center.

Kostyshyn reminds the students that these requirements reach well beyond the building. The access route for fire trucks may decide where a building can stand on its site, whether a courtyard can be closed, and how a landscape is paved. At Greenway Homes, the fire department will reach the courtyard on foot, through the gate on Aldous Street, but its trucks will stay on Marlow Street, Aldous Street and the lane, so every entrance and the fire department connection must be within reach of those streets.

Exercise 8: sprinklers and fire alarm

• Identify the sprinkler standard and hazard classification for each space in your Design Studio IV project.
• Locate the sprinkler room, the fire department connection, the standpipe hose connections and the fire alarm annunciator on your plans.
• Draw a reflected ceiling plan of one room with exposed structure, showing sprinkler heads at the code's maximum spacing.
• Describe how the alarm will notify a deaf resident asleep in an apartment.

Self-check

• Have I planned space for every fire protection room and device, not just drawn heads on a ceiling?
• Have I considered freezing in every unheated space with sprinkler piping?
• Can the fire department reach every entrance, connection and stair?