Most fire codes  depend upon the National Fire Protection Association guidebooks.  In turn these propose the use of simple zone models that solve conservation of mass and energy in a control-volume sense for each zone. One weakness of zone modeling is that momentum conservation is only captured through use of loss coefficient at openings. The strength of zone models is that they are very fast compared with computational fluid mechanics (CFD) based models. Multi-level Atriums are examples of large spaces for which these conventional zone-model approaches are not always effective. CFD, sometimes called “field-modeling” in the fire community to distinguish it form zone-modeling, has an unparalleled potential as an engineering estimator of fire consequence in atria since it permits specification of momentum conservation as well as much finer spatial and temporal resolution. Fire physics is the key to the approach. In addition, CFD approaches provide a link between outside building weather conditions and fire and smoke development. In large-volume spaces such atria, smoke management systems are often an important aspect of fire protection, with their primary goal being to ensure that the impact of smoke and heat on occupants is not life threatening (NFPA 92B). This involves keeping the height of the smoke layer above the highest level of occupancy for a defined period, longer than the expected time to evacuate the building. Atrium smoke management relies on the buoyancy of hot smoke rising above a fire. As it rises, relatively cool ambient air is entrained into the plume decreasing the temperature and increasing the mass flow rate of contaminated air. Upon reaching the ceiling, the momentum of the plume is diverted into a jet which spreads the smoke over the ceiling area. Long travel distances and architectural features can cause further entrainmen tof air, adding to the smoke filled volume. Once the ceiling jet has covered the ceiling, the depth of the smoke layer increases until either the atrium fills with smoke or the rate of smoke entry into the layer is balanced bythe rate of exhaust. Make-up air must be introduced below the smoke layer and should not generate turbulence in the vicinity of the plume or smoke layer, since this would tend to increase the  required exhaust rate. This often means that make-up air should be provided from a wide distribution of supply points over the lower levels of the building to keep air speeds below 200 feet per minute within the atrium. In some situations, make-up air can be used to provide a degree of protection for egress routes. The design of an effective smoke management system requires calculation of smoke mass flow rates and rate of descent of the smoke layer. It is particularly important to consider the time from ignition of the fire until detection, after which the system would be expected to control further growth of the smoke layer. A starting point to estimate quantities of smoke from a fire is the empirical formulae listed in applicable building or fire codes, or the NFPA 92B.

 

BLE SD series smoke curtains are the gold standard of the smoke curtain technology. Underwriters Laboratories listed, patent pending technology which provides an automatic gravity fail-safe smoke barrier invisible under non-fire conditons. In a fire scenario, the U.L. listed smoke curtains deploy by a signal form the fire alarm system or loss of power or communication from the fire alarm system simulating fail-safe and provide a physical barrier to smoke and compartmentalize or datum  the smoke by reducing horizontal smoke and fire migration. Desgined to develop datums six feet  eight inches or six feet above the finished floor. This allows for more freedom of design for architects to draw more ambitious and unique atriums open to above and below on multiple levels while still complying with the IBC. Smoke  draft curtains are designed to develop datums six feet above egress-able horizontal  walking surfaces and hold the boyant smoke layer of smoke for calculated amounts of time, allowing for occupants' safe egress to the accessible exits. Life safety joined with design—a winning combination for all. This mitigates the requirement for mechanically supplied make-up air for an atrium smoke exhaust system. Typically, we have been able to reduce exhaust requirements in half by use of curtain technology (see case studies) thus reducing the need for larger volumes of make up air. Mechanically supplied make up air for an atrium design fire is expensive and not fail safe.