Research: Smoke Management – Malls, Sprinklers and Smoke

In North America, it has generally been assumed that communicating spaces connected to an atrium or mall will be sprinklered and, as a result, the sprinklers will limit the size of a fire in the adjoining space. As a result, engineering design guides for smoke management systems such as National Fire Protection Association NFPA 92B1 have assumed that the smoke will have minimal effect in the atrium or mall space. The design guides, however, do allow for smoke management designs in which the smoke is allowed to spill into the atrium space.

With the introduction of performance-based designs for fire protection systems, there has been an increasing need to address the potential effects of smoke entering the atrium or mall. There have been concerns that smoke cooled by sprinklers in retail spaces connected to malls could travel downward, where it could endanger people evacuating the building.

In a recent joint study with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the National Research Council of Canada investigated smoke movement from fires in sprinklered retail spaces linked to a mall.2 & 3 A large-scale test facility was set up to simulate areas of particular concern: a retail outlet on the second floor and a section of a pedestrian mall in a shopping centre. Because North American fire statistics indicate that approximately 90 per cent of fires in retail facilities activate four or fewer sprinklers,4 four sprinklers were used in the retail portion of the test facility. The mall portion of the test facility included a mechanical smoke exhaust system.

Tests were conducted to simulate retail fire scenarios with the fuel shielded from direct water spray from the sprinklers. The scenarios were typical of those that occur in retail stores in malls and included clothing and toys in boxes located in display units, and stored or displayed bulk goods, such as paper towels.

The resulting fires had three distinct phases: fire growth and sprinkler activation; steady fire; and decay. During the fire growth phase, all four sprinklers were typically activated within five minutes and hot smoke flowed into the mall portion of the test facility.

During the steady fire phase, hot smoke continued to flow into the mall area and a smoke layer formed there even though the smoke exhaust system was in use. Hot smoke flowed into the mall area for up to 20 minutes depending on the test conditions. The optical density of the smoke in the upper portion of the simulated mall and its carbon monoxide concentration both exceeded tenability limits. Any accumulation of this smoke in exit routes could limit evacuation.

During the decay phase, the smoke was cooled to near or below ambient temperature.

The cool smoke was mixed throughout the fire compartment, i.e. it was in the retail portion of the test facility, and spilled through the opening and descended into lower areas of the mall portion.

In addressing concerns that smoke cooled by sprinklers in retail spaces connected to malls could travel down and endanger people evacuating the building, the results of the study indicate that during the initial stages — fire growth and steady fire phases — the smoke entering the mall area is hot and rises towards the ceiling. A smoke management system using mechanical exhaust could be used to remove this smoke.

During the decay phase of the fire scenario, the optical density for the smoke in the mall area approached or exceeded tenability limits. The rapid mixing of smoke throughout the fire compartment in or near the opening into the mall area during this phase could trap any occupants still in the area. However, the extent of the smoke zone was limited and occurred during the later stages of the fire after occupants should have evacuated the fire zone.

Gary Lougheed is a senior research officer in the Fire Risk Management Program at the National Research Council’s Institute for Research in Construction in Ottawa. Cameron McCartney is a technical officer in the same program.

1 NFPA 92B, Guide for Smoke Management Systems in Malls, Atria, and Large Areas, National Fire Protection Association, Quincy, MA, 2000.

2 Lougheed, G.D.; McCartney, C.; Taber, B.C., “Smoke Movement for Sprinklered Fires,” ASHRAE Transactions, Volume 106, pp. 605-619, 2000.

3 Lougheed, G.D., McCartney, C., Taber, B.C., “Sprinklered Mercantile Fires,” ASHRAE Transactions, Volume 107, pp. 730-743, 2001.

4 Johnson, P., “Shattering the Myths of Fire Protection Engineering,” Fire Protection Engineering, Issue 1, 1999, pp. 18-27.