Big Box Stores and Fire Protection
The sprawling precast stores and distribution centres seen across Canada present challenges for fire protection owing to the contents and equipment they contain.
From the January-February 2015 print issue.
The sheer size of “big box” stores and distribution centres puts them beyond the prescriptive limits of most fire codes. That leaves designers like Adam Nadem, AIBC, AScT, an associate principal at Vancouver’s GHL Consultants, preparing “alternative solution reports” and finding applicable codes in other jurisdictions.
And designing fire and life safety systems for these large buildings has other challenges: the merchandise consists of everything from paint and construction materials to soft goods, household cleaners and plastic furniture. Large quantities of these goods are stored on racks 25 feet high or more; there is a potential for exit paths to be blocked by automated cranes, conveyors and storage systems; and finally changes in the tenancy or layout can abruptly cause fire code violations.
A typical big box store by one definition is over 8,000 square metres, with precast walls containing rigid insulation. Its wall to roof ratio might be 0.3 per cent, its wall to window ratio 7.5 per cent. The building is likely heated and cooled by rooftop units. The majority of the floor area is dedicated to sales, but there are small sections for offices, storage, receiving and a greenhouse.
Code issues arise when local codes may not address either the type of material or the method of storage in these facilities. Nadem has been involved in projects where elevated rack platforms with multi-level mezzanines essentially created a four- or five-storey “building within a building.” Building and fire code compliance in such a case is usually based on an alternative solution using additional standards: some international, some from other provinces. “Some local authorities will allow us to use other codes, some won’t,” Nadem says. “It varies from one municipality to another.”
Fortunately, codes are moving more towards being performance-based rather than prescriptive. “The design has to meet the same performance objectives as those indicated by the prescriptive requirements,” says Nadem. As a result, fire modelling (to determine how long it would take for fire to make the building untenable) is being used more and more to establish that performance-based codes can be met.
Timed exit studies (using data from industry programs, engineering judgement and technical organizations like the Society of Fire Protection Engineers) are also vital tools for meeting code requirements in big box stores and distribution centres.
“Automated crane and storage systems obstruct normal code-required egress paths, resulting in a longer travel distance to exits,” says Simon Crosby, CET, project manager at Toronto’s RBA Engineering. He uses data from timed exit studies in these instances. Distribution centres also have equipment such as massive conveyors running at ground level that may lie in the way of exit paths, presenting a fire-safety challenge.
Sprinkler coverage is also a major issue in stores that can have 35-ft. ceilings and 25-ft. shelving racks holding double rows of a wide variety of goods, all mixed together. “Group A” plastics represent the worst-case commodity in storage, says Paul Wagner, P.Eng., senior associate at LRI Engineering in Toronto. These highly combustible plastics melt quickly and create toxic fumes. The International Code Council describes them as “plastic materials having a heat of combustion that is much higher than that of ordinary combustibles.” Group A includes such common materials as ABS, fibre-reinforced polyester (FRP), acrylic, butyl rubber, polystyrene, polyurethane, PET and PVC. Special sprinkler systems are required to meet building codes for these materials in this type of storage.
“NFPA 13 design parameters (a National Fire Protection Association code, referenced by Canada’s National Fire Code), which call for Early Suppression Fast Response (ESFR) sprinklers, 20 psi minimum water pressure and one-hour water-supply duration, avoid the need to add in-rack sprinklers. They minimize the water pressure required at the sprinkler heads, and hence the need to add a fire pump to the facility,” Wagner says. He adds that if the ceiling and storage heights exceed 35 ft. and 25 ft. respectively (which many do), a different sprinkler design is required.
GHL’s Nadem points out that in the case of shelving racks with in-rack sprinklers, an employee could block the flues between shelves simply by adding an extra row of boxes, and thereby violate the fire code. A change in tenants or layout (such as splitting a space with a wall, completely altering the means of egress in an emergency) can also suddenly render a building non-compliant, he says.
From an alarm system perspective, big box facilities don’t offer many challenges. Smoke detectors are generally only placed in offices and electrical, computer and lunch rooms, rather than in the store itself, says John Gallo of Mircom Group. Horns and strobes for notification are placed on pillars throughout the store (two to four per pillar); 50 to 60 fire alarm pull stations per store is not uncommon.
Gallo says there has been an increase in the number of addressable systems installed in the last six years. Conventional panels are still the norm for smaller applications, but intelligent panels offer the benefit of identifying exactly where the problems is: each device has an individual address, so firefighters and staff can identify the exact location of an individual device that is signaling an alarm or a malfunction. cce
Sophie Kneisel is a freelance writer based in Baltimore, Ontario and a former editor of Canadian Consulting Engineer magazine.