Building code requirements for an atrium are provided in section 404 of the IBC. There are 8 basic requirements outlined in section 404. In summary:
- The use of the atrium space is limited to low fire hazard
- The entire building must be equipped throughout with an automatic sprinkler system
- The entire building must be equipped throughout with a fire alarm system
- Smoke Control is required in the atrium
- The atrium must be separated by the rest of building with a minimum of a 1-hour fire barrier
- The Smoke Control system is required to be connected to standby power
- The interior finishes of the atriums are limited to be not less than Class B
- Travel distance through the atrium is limited to 200 feet
Often, the most difficult component to provide is Smoke Control. The smoke control system must be engineered specifically for each project and can vary greatly depending on the layout of an atrium and the fire hazards contained therein. The goal of the smoke control system is to maintain a tenable environment for building occupants. This typically includes maintaining the smoke layer 6’ above the highest occupied floor for 20 minutes. A smoke control system consists of 3 basic components.
- Exhaust Fans: The top of a smoke controlled atrium is typically lined with louvers connected to very large exhaust fans. Smoke and fire modeling is used to determine the exact size of the exhaust fans but it’s not unusual for exhaust fan requirements to exceed 200,00 CFM. Fans of this size are very expensive to purchase and maintain. Often, the size and weight of the fans will also require additional structure and roof space.
- Auxiliary Power: The exhaust fans are typically required to operate for 20 minutes on emergency or auxiliary power. The power draw from these fans can create a significant increase of size and cost in the generator system.
- Make-up Air: If a smoke control system is to exhaust 200,000 CFM of air out of the atrium then 200,000 CFM of air must be supplied back into the atrium. As a rule this air must be provided low and slow. A 200,000 CFM exhaust rate would require 1,000 square feet of openness on the ground floor of the atrium to meet make-up air requirements. That is equal to (48) 3’x7’ doors on auto openers. Most buildings don’t have 48 doors that can be used for make-up air so actuated windows or louvers are typically used in conjunction with doors. This can be very expensive and difficult to design around and can severely decrease building security.
Design:
The goal of this design was to provide a 3 story atrium that is completely open to all floors. This space was retrofitted into an existing building and it would have been extremely difficult and expensive to install a smoke control system. Through the use of Smoke Guard’s M4000, the design team was able to maintain 3 open stories while avoiding the requirement for a smoke control system. This was done by utilizing an exception in the atrium requirements that eliminates the need for Smoke Control for atriums that only connect 2 stories. The M4000 was used to completely surround the top level of the atrium creating a 1-hour rated atmospheric separation between the third level and the lower two.
The M4000 is activated by fire alarm or loss of power and allows the space to be open during regular operation but be separated during a fire event. This allowed the design team to take advantage of the exception that eliminates smoke control in two story atriums.
Why the M4000:
Smoke Guard’s M4000 offered the most flexibility in this open design. Traditionally, this approach to eliminate smoke control would require enclosing the atrium with glass or breaking it up with columns, walls and vertical acting coiling steel fire doors. These traditional approaches would have detracted from the open design and created unwanted separation. The M4000’s low profile easily fit above the ceiling and its ability to make turns allowed it to encapsulate the atrium without the need of side guides or exposed structure.
