Canadian Consulting Engineer

Speaking Out: Open Air Parking Garages

The rules in the National Building Code of Canada for the fire protection of large open air parking garages can result in costly and unjustified designs.The requirements in the current -- 1995 -- edit...

May 1, 2003  By Demir Delen, P.Eng., Morrison Hershfield

The rules in the National Building Code of Canada for the fire protection of large open air parking garages can result in costly and unjustified designs.

The requirements in the current — 1995 — edition of the National Building Code of Canada (NBC) for large, multi-storey, open-air garages demand a level of performance that is not justifiable by any study, test or past performance. Nor do these requirements make for cost-effective fire and life safety design.

The National Building Code recognizes the low fire hazards associated with open-air parking structures and relaxes a number of passive and active fire safety requirements that apply to other types of buildings. However, the code only eases the rules to open-air parking structures that are not more than 10,000 square metres in building area and not more than 22 metres in height.

Open-air parking garages are being constructed in airports across Canada with building areas far in excess of the 10,000-m2 limitation. Because these structures exceed the area limit, they are subject to the requirements for a large industrial occupancy. No recognition is given to such parking garages’ extremely low hazards, the transient nature of the parking use and their low occupant load.

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The basis for the 10,000 m2 area limitation reflects an earlier assumption by the Standing Committee on Fire Safety in Buildings about the maximum possible size of these structures, related to the dimensions of a typical city block. Because the current National Building Code is not objective-based, any open-air parking garage that exceeds the limit is subject to requirements that do not relate to the actual hazards associated with the increased area.

The National Fire Protection Association Handbook states that the fire load and hazard from private automobiles is very low, despite the presence of gasoline and combustible tires. It further states that where parking structures have permanently open exterior walls that can dissipate smoke and hot gases, the likelihood of a serious fire is extremely low. Surveys of actual fires experienced in open parking garages have confirmed that the incidence of fire is infrequent and the fire severity is low. Actual fire tests demonstrate that even when a car is gutted, the fire does not spread to the adjacent cars and the overhead structure remains essentially unaffected.

It follows from the above that when the building area of an open-air parking structure is increased beyond 10,000 m2, the only change needed is a proportional increase in the number of exits due to the increased occupant load and the travel distance requirements. All other fire and life safety requirements should remain the same. Despite this, the NBC requires an open-air parking garage with a building area greater than 10,000 m2 to have additional fire and life safety features. Some of these have a significant effect on design and cost, as follows:

the open-air parking garage must be protected with dry sprinkler systems

a fire alarm system must be installed

floors must be constructed as fire separations.

The requirement for floors in large open-air parking garages to be constructed as fire separations having a one-hour fire resistance rating prohibits any vertical openings other than vehicular ramps. The rule means that open stairs, escalators or lightwells would not be permitted. Yet, these features may be important, especially for parking garages at airports.

From a fire safety perspective it does not make sense that a small stair or escalator opening in the floor assembly of a large open-air parking garage is prohibited, whereas much larger openings for vehicular ramps are permitted. The generation of smoke is an issue related to the hazards associated with the use of a building, not its size.

To make matters worse, even the expansion joints on the concrete floor have to be provided with suitably rated fire stopping materials since the code requires the floor assembly to be a fire separation with a one-hour fire resistance rating. In one particular airport parking garage, considerable time and money were spent to design and test a suitable fire stopping material for the narrow expansion joints adjacent to very large openings for vehicular ramps that were allowed to be unprotected. This work was in addition to providing sprinkler systems in the open-air parking garage in order to comply with the code requirements.

Considering the low level of hazards associated with open-air parking garages, the U.S. National Fire Protection Association developed the 88A Standard for Parking Structures to address the fire and life safety requirements specifically for such buildings. An open-air parking garage with a building area greater than 10,000 m2 and height greater than 22 metres can be constructed under this standard with no sprinkler system, no fire alarm system and floors not as fire separations. Even the travel distance to an exit can be increased to 120 metres from the 45 metres the National Building Code prescribes.

It is hoped that with the upcoming introduction of the objective-based National Building Code of Canada, the construction of large open-air parking garages will be made more cost-effective and in line with the fire hazards they present.

Demir Delen, P.Eng. is a principal and director of fire protection engineering with Morrison Hershfield of Toronto.

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