Life safety is the most important part of every building’s occupancy certificate. The delicacy of a correctly operating life safety system is paramount to the safe working environment for a building’s occupants. The objective of the life safety system, particularly the stair pressure systems and their zone smoke control, are to create and maintain a clear, smoke-free path long enough for a building’s occupants to safely evacuate in the event of a fire. There are multiple trades and multiple roles within a life safety bid, testing, and proving to be operating correctly.
Below, we will examine two parts of the life safety system: stair pressurization and zone smoke control.
Design Challenges
During the design phase, the number one challenge a design engineer will encounter is physical space. This determines the physical attributes of the stairwell and its eventual configuration. You may have two separate fire stairwells on opposite sides of the building. Or perhaps a scissor stair scenario with multiple entry points from a tenanted space. From a design perspective, this is the first crucial element of the design process.
Equipment selection is not always an easy task. The system designer will try to account for pressure losses of the air paths as well as the equipment the air must pass over and around. In most cases, the designer will allow for more static on the fans to guarantee adequate supply in the worst-case scenario. But is that enough? What about the outside wind conditions? Are the adverse weather conditions that are historical to the area detrimental to performance of the system? Has the architect taken into consideration these weather conditions?
From a commissioning (Cx) perspective, the design phase is a busy time. The commissioning authority will need to review each portion of the design process carefully. The physical location can be a major challenge for a life safety system. Pressure control must be taken into consideration.
Stair pressurization fans and stair relief fans can and will control perfectly to their respective pressure setpoints as long as the pressure from the space to atmosphere is stable. Structural obstacles such as balconies, inlet louvres, etc. can wreak havoc on the atmosphere reference point.
The structural integrity of each stairwell is another key element of pressure control. If pressure increases in one zone (whether it be stairwell or fire compartment) and there are leakages between these spaces, it will be very difficult to control the HVAC systems. The use of enclosure testing and thermal imaging could be a very useful tool during this phase of commissioning.
The electrical performance of each fan and relay will need to be tested against a fire matrix to ensure that every piece of plant and equipment operates as nominated. Following on from this, the functional performance testing will need to be carried out with the fire interface panel to make sure that both the HVAC systems and the fire protection systems are working together correctly.
The project should now be in a phase of testing actual performance. It is not uncommon for the local jurisdiction to be involved in this process. There are local authorities that utilize specialized smoke systems with applied heat to simulate the buoyancy of hot smoke during a fire scenario. Quite often, in these types of tests, the visual performance is easier to follow than the documented test results.
Assuming that all of the above has been completed, the testing, adjusting, and balancing (TAB) professional will be invited onsite to test the actual performance of the life safety systems and report on the findings. Unfortunately, in most instances, a project is not ready, and the TAB professional will end up testing multiple stages multiple times as the construction process unfolds. With unforeseen delays to the construction process, and perhaps contractual agreements allowing the owner to occupy portions of the project during construction, we quite often see a staged handover of the life safety systems implemented on a project.
The TAB professional will test each system for performance and apply their testing against criteria taken from the specified test parameters listed in the specified contract documents.
Test Criteria
There are countless codes and standards that a commissioning agent and TAB professional must be aware of. It is extremely important that the test criteria for the building, whether it be a new build or an annual recertification test in an existing building, is available to review and discuss.
As obvious as this comment may be, it is imperative that the standards you are testing to are both known and understood by all parties involved. Each standard should be read carefully, and any “gray” areas discussed prior to commencement of work. It is always better to read a standard literally rather than twist its words to suit your situation. The systems we are testing are designed to save people’s lives. We most certainly DO NOT want to cut corners or risk system failure to save a bit of money.
Each set of contract documents should list the intent of the life safety system performance from the fire engineer on record or the authority in charge of this process. All questions should be forwarded to this same person for action and response.
A common standard followed in Australia is AS 1668. However, in California for example, the California Building Code must be adhered to. Although both standards differ, they both share a common goal and strategy by manipulating ventilation systems to achieve suitable smoke control. Both standards refer to differential pressure requirements, door opening force requirements, and smoke layer requirements, etc.
Construction Challenges
During construction, issues will definitely be encountered. How we mitigate that risk and apply quality control is the difference between a successful outcome or a painful and drawn-out process. Time is key. Not only from the perspective of needing “more time to do the job,” but allowing each process the suitable amount of time to see the task completed correctly.
General contractors are reliant on mechanical contractors to “get it done” when it comes to the HVAC systems. However, they often don’t want that to involve interference with their structural work.
Although general and mechanical contractors must coordinate meticulously throughout the construction process, it is at this point where the harmony of both must be at their absolute. The life safety system can often be the key to occupancy and the final hurdle of the project. Cooperation from the general contractor and understanding from the mechanical contractor is paramount.
Testing Challenges
As discussed in the sections above, communication and coordination are the keys to a successful life safety test. However, unfortunately, the initial test(s) are more of a quality check exercise for the Cx and TAB agents as they navigate the tasks that were missed or not yet completed due to various reasons. Pressure control is arguably the biggest concern for the TAB company.
The TAB professional must ensure that a valid and suitable setpoint is obtained for all relative fans associated with the stair pressurization system. But what is the setpoint and how is one achieved? Just as with TAB work itself, a series of tests are carried out on what experts can predict as our worst-case scenario fire door(s).
The aim for the TAB professional is to operate the system only as hard as required to achieve the desired acceptance criteria. This set of equipment data becomes our baseline parameters. From here on out, the test should run quite smoothly, and only minor adjustments to these setpoints are to be expected.
However, a further challenge encountered is where one extreme becomes too great for the other extreme. We must run the fans at maximum speed to achieve our door velocity minimum requirements which creates too much pressure on other areas preventing doors from opening. Depending on how a TAB professional carries out the test, a rogue door opening force could cause a major headache and significant retesting time.
Another remarkable yet extremely common challenge encountered by a TAB professional is simply adverse weather conditions. It is not uncommon for a test or annual compliance test to be postponed due to unusually high winds outside. Outside wind blowing into a fire stairwell can wreak havoc on our stairwell sensors. Although there are products available to reduce the impact of this type of scenario, it quite often is not enough, and the test must be re-attempted on a more suitable occasion.
Solutions
Setpoints
A solid baseline is not an easy task in a lot of buildings. In fact, such as hospitals and other complex design scenarios, the perfect setpoint might be extremely challenging. To be able to find a setpoint that works well for every scenario, it can often pay to think outside the box and create a solution to a problem.
During the design phase, it is best practice to include both TAB and Cx professionals in design discussions. The TAB and Cx professionals have encountered many different challenges and configurations and being able to draw from their experience could save a lot of time and money up front.
Building smart is also a great advantage in a successful stair test. Overcoming multiple setpoint challenges by installing a valves system is one of the smartest design ideas I have witnessed. With simple wiring and copper tubing, a 100+ level building can be configured to have every fire-affected floor referenced to atmosphere, ensuring that a fire door close to the fan will not have too much fan speed and pressure applied to that particular zone fire trip.
The worst-case scenario, however, would allow the fans to drive to the maximum to accommodate the increased performance requirements. As long as the atmosphere reference is in a suitable location and reliable, this control system will all but guarantee future performance.
Door Opening Forces
How often have you worked your way through a building only to find an issue with a door that requires a revisit or retest? I have experienced this on too many projects over the past 22 years. A carpenter or door hanging contractor often isn’t made aware of the requirements that depend on the way the door is hung and hardware set.
Depending on the door opening force required in a specific region, a “passive” door opening force requirement can be established. For example, a good “passive” setpoint for a fire door in Australia is around 50Nm. This will allow a door to close under minimal pressure but not apply too much pressure, preventing the door from opening in a fire.
Another challenge often faced is a fire door catching on the frame or rubbing on the concrete landing on the other side of the door. These deficiencies are noted, and the doors will have to be corrected and subsequently retested. However, a TAB and Cx professional can often verify system performance as a noted interim test.
Experience tells me that I can hold the door on the edge of the frame to allow the stair fan to back off to its minimum and then retest the opening force. Although this cannot be the final test, it will give me confidence that the system setpoint is adequate and the system will work once the deficiency is rectified.
Pressurization
As discussed, system and building pressures present their own respective challenges. We have already mentioned the smart building solutions with a valve and tube solution but what about establishing suitable pressures for multiple fans?
Once a fire trip is initiated, each fan will control to its minimal setpoint, waiting for instruction from the cause and effect of a door opening or closing. When all fire doors are closed, we want our stair fans to operate, but only to the minimum allowable speed. This will allow the fire alarm instruction over the evacuation system to be heard, understood, and followed.
Once the building’s occupants respond to the alarm system, the most common action is to descend the fire stair to safety. This means opening the fire door. We DO NOT want too much pressure! This could prevent an occupant from opening the door and could end in tragedy. We also do not want the fans to be completely off. The time taken for the stair fan(s) to start could be too long, allowing smoke to enter the stairwell. This is why we have the fans turning over to their lowest possible speed. This will ensure the fans are ready to ramp up and also prevent motors from burning out.
If stair relief fans are used, they must also operate to their setpoints, which will be the pressure required to remove the stair pressure fan(s) volume, along with any smoke, safely out of the building. However, these fans hold the potential to move large quantities of air through an opening, which could prevent the damper blades from opening or even push a set of smoke control damper blades out of its frame.
Careful consideration is required, and it is common for the use of time delays to allow for the damper to be fully open before operating the fan. The fan will be able to maintain its setpoint easily in a passive state. However, when the fire door is opened, the relief fans will respond to the pressure decrease and ramp up to assist the stair fans with the smoke control.
In a similar situation, to that of the physical door opening force, the stair pressurization and stair relief fans need to be carefully configured to accommodate the worst-case scenario, as well as our best scenario, and of course everything in between. The TAB professional must first establish the worst performing door and ensure the system will respond to pressure increase and decrease and respond accordingly to allow the door to open and then provide sufficient air movement to keep smoke out.
Conclusion
Life safety is a process that requires attention to detail, careful planning, clear and concise communication between all trades and cooperation by the entire project team. This is a particular task that involves everybody, and the principal contractor and sub trades MUST be managed correctly to ensure this process’s success.
An owner’s representative’s best friends are the TAB and Cx professionals. They will have the skill, knowledge, and experience to deliver the successful system operation in a timely manner; however, authority is key. The TAB professional, in this case, should not be needed, as the Cx professional will discuss issues with the project team during the design phase. Addressing any concerns in the kickoff meeting and laying down the expectations from the owner’s project requirements brief to the entire team of sub trades life safety on a project is the collective responsibility of every worker on the job. If each phase of the commissioning process is given suitable time, focus, and energy, a successful outcome is a more likely outcome.
