Given the current environment, it is necessary to have a collaborative effort for today's fire/smoke design. In addition to the traditional professionals such as architects and mechanical and electrical engineers, other design team members include an independent code consultant/specialist, fire protection consultant/specialist, and a computational fluid dynamics (CFD) engineer/analyst, and of course, the AHJ. Many of today's fire and smoke control issues and team member roles for collaborative design are changing and growing.
A Front End Code Survey
A good place to start any project that involves a collaborative effort is with a front-end code survey. A front-end code survey is critical in order for all team members to have a working knowledge of the applicable codes on the project. Too often, design team members begin their respective designs without knowing exactly which editions of the NFPA, model building codes, or local ordinances apply to the project. The code survey is best conducted directly with the AHJ who has responsibility for the project. It is important that the interpretations of the local AHJ be documented and distributed to all design team members. A standard front-end code survey can identify "lessons learned" from previous projects and ease the pain of repeating previous mistakes.The report should be distributed to every member of the design team. It should include specific questions related to code interpretation by the AHJ regarding sprinklers, standpipe systems, outside fire protection, miscellaneous fire protection requirements, HVAC smoke control issues, fire and smoke damper requirements, electrical and plumbing utility information, and even items outside of codes that are necessary to determine on the front end of a project. This form allows each design team member to understand that there is a common coordinated effort related to the building codes, and it shows how that effort will affect the design of the fire and smoke control systems.
If the project involves a code consultant, the code consultant would conduct the front-end code survey project report. If the project does not involve a code consultant, other members of the team will need to handle the report.
Occupancy Classification
One of the first things that must be done is to determine the building's or project's occupancy classification. The architect, rather than the engineer, will ascertain the occupancy classification, and the architect's direction will ultimately affect the design of the entire building. It is the very first thing that has to be determined in the plan, and the AHJ, the architect, and everyone on the team must be concerned with the occupancy classification, as it will affect each of them throughout the project.Each occupancy classification carries a different set of design criteria that affects the fire and smoke system's design. In high-rise buildings, the fire alarm system must include audible and visual annunciation such as pre-recorded measures instructing building occupants how to exit the building in case of an emergency. The AHJ or fire department may require a general alarm or may desire annunciation for exiting to a limited part of the building. Also, in high-rise classifications, other design elements include elevator recall, a fire command center, and firefighter's telephones. Depending on the classification, emergency generators for pumps and other equipment will be required.
In arenas and other large assembly classifications, the fire alarm annunciator may be delayed to allow building operators a chance to respond to an alarm condition prior to a general evacuation message. In active smoke control systems used for a smoke-protected egress, it may be permissible to eliminate fire dampers. In other jurisdictions, remotely resettable fire dampers may be required. These are just a few of the many issues that relate to the occupancy classification and, again, the entire design team must collaborate on the common design solutions.
Fire Protection Design Issues
Most buildings today require fully sprinklered buildings. With fully sprinklered buildings, exit travel distances are increased, and the fire ratings on walls are typically reduced. For example, corridors previously had to be one-hour rated. Now, they can be built as smoke-tight construction only. Requirements for fire and smoke dampers are definitely affected when buildings are fully sprinklered.Another change in the industry is that more and more states are requiring the engineer of record to perform hydraulic calculations. In the past, the engineer of record would prepare a performance specification only, and the sprinkler contractor would perform the hydraulic calculations. Now, the engineer of record's role is expanding. The drawback to this is that the knowledge base in fire protection design traditionally rests with the sprinkler contractor rather than with a registered engineer. The engineer is doing something now that he may or may not have specific expertise in. The design team may have to involve a sprinkler contractor or a fire protection engineer/specialist as a member of the design team.
The front end code survey should determine whether the state requires full sprinkler system design as part of the contract documents, including hydraulic calculations, or if the engineer of record can prepare performance specifications only. The architect may want to include a fire protection engineer on the design team, depending on the state requirements.
Active vs. Passive Smoke Management
There are two choices when designing the smoke management system in a building. One is an active smoke management system, and the other is a passive smoke management system. As implied, the active system utilizes the building's HVAC system or dedicated equipment to control smoke migration in case of a fire.Passive systems are less complex to design and have historically been used wherever possible. Many buildings today, however, are designed with smoke-protected egress, which requires active smoke management systems.
Active smoke management systems are used in high-rise buildings, large assembly areas, and arenas. They are also used in high-rise buildings, for example, because when the fire floor is exhausted, the floors immediately adjacent to the floor are pressurized so as to contain the smoke migration to the fire floor or compartment. In this situation, the entire team must be involved because many systems are affected in active smoke management systems. Particularly, the AHJ must agree with the conceptual design parameters of the active system design.
In assembly occupancies, for example, the design team may elect to use smoke-protected egress. In smoke protected egress, exit widths for stairways and corridors are significantly reduced. This is a case in which consulting with everyone on the design team will benefit the project. As the systems become more complex, more expertise is needed to make the best decision for the project. Often, this variety of expertise requires a diverse team of design professionals.
Dynamic vs. Static Fire/Smoke Dampers
Another area of consideration is that fire and smoke damper specifications can no longer be simply designed by the mechanical engineer for the project without consulting other team members. Traditionally, all the mechanical engineer had to decide was the rating of the damper to specify based on the wall. For example, a one-and-a-half-hour damper would be installed in a two-hour wall.Today, the mechanical engineer must select and specify fire, smoke, or a combination of fire and smoke dampers for a multitude of criteria. First, fire dampers must be selected for either a dynamic or a static rating. Static dampers are used in systems that will close with no air pressure. Dynamic rated dampers are used in systems that must close when the duct system is under pressure. This criterion will be highly dependent upon whether an active or passive smoke management system is used.
One major factor with fire and smoke dampers is the maximum size of the damper. UL testing now limits the size of the dampers, so all team members must be aware of the maximum damper sizes, as it will affect damper opening sizes throughout the building. Because we can't design a damper of unlimited size, the maximum size limitation must be coordinated with the architect. In some cases, multiple smaller sizes must be provided rather than just one large duct opening.
Sometimes, in a haste to get everything done, the maximum size of the damper is overlooked until it is out in the field, when it can become a very costly mistake. It is better to address this up front by collaborating with the team early in the design, rather than figure it out in the field after the dampers have already been purchased or, even worse, installed.
The AHJ should have a say in whether dynamic or static dampers are used throughout the system. The mechanical engineer must decide if dynamic dampers are required even with passive smoke management systems. The reason for that is because the fire damper may be forced to close before the fan systems can be shut down by the fire alarm system. Again, input from other design team members on how the system will function is necessary for each step of the project.
BAS and Fire Alarm Interfaces
Another system that requires collaboration today is the design and interface of the fire alarm and BAS. It was often all too easy in the past for the electrical engineer and mechanical engineer to work independently of one another until the very end of a project when they finally had to sit down and coordinate the type of interface between the two systems. The interface previously was very simple, requiring only a hard wire connection from the fire alarm system to each major piece of mechanical equipment.Today, collaboration is mandated due to the increased complexity of both the fire alarm and BAS. The interface required today may be at the network level of each system rather than at the equipment level. There have been many recent articles discussing the advantages and disadvantages of how to specify the fire alarm and BAS interface.
Traditionally, fire alarm systems have all been specified with proprietary interfaces. Today, with the ASHRAE BACnet protocol, fire alarm systems and BAS can coexist on the same network, resulting in a more seamless interface. The electrical/mechanical engineers must decide how connections to smoke dampers and other HVAC equipment must be made. The AHJ will also influence whether the fire alarm system or the BAS activates or de-activates dampers and equipment. Again, a team effort is required in this process.
A Collaborative Effort
These are just a few of the issues pointing to the need for a collaborative effort in fire and smoke control system design. This collaborative effort is not a casual one. It should be reinforced throughout the design of the project to ensure that all team members are proceeding in the most effective direction.The architect, mechanical engineer, electrical engineer, and AHJ are obvious team members who must work closely together to ensure that the life safety systems meet the intended functional requirements of the facility.
Each member of the team should be familiar with the issues that affect other team members. All team members should be attentive to the issues of other disciplines and be ready to provide constructive input in the total solution for the fire and smoke control design.
Summary for Part Two
In this article, which is the first in a series, we discussed the roles and issues of traditional design team members including the architect, mechanical and electrical engineers, and the AHJ. More and more projects require additional design team members to facilitate a full understanding of the complex issues related to fire and smoke control design. A specialist in code consulting is frequently needed to present code equivalencies to the AHJ and get ‘buy-in' to the proposed fire/smoke control approach for the project. The architect and other team members often have so many of their own design issues and tasks that the code issues become too casual and are overlooked. A code specialist is mandatory on certain projects such as arenas, theaters, large shopping malls, or hospitals.It was not too long ago when the mechanical engineer could size the smoke management system for an atrium by simply calculating the volume of the atrium. The building codes were prescriptive when determining the capacity of the smoke management systems. Today, a more complex set of equations is mandated by the codes to determine the design fire size, its resultant smoke generation capacity, and the corresponding size of smoke management equipment. In lieu of NFPA 92B methodology, CFD analysis by a CFD analyst may be warranted.
Part two of this series will discuss these issues and give specific project examples. ES
