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Understanding the Basics of Smoke Control Systems

Navigating Through Fire: An Insight into Smoke Control Essentials

Smoke is among the most serious hazards that can occur within a structure. While fires can cause significant damage, it’s often smoke that results in the majority of injuries.

For the safety of inhabitants, along with safeguarding furnishings and equipment from potential smoke damage, it’s imperative to have a smoke control system in place.
This system regulates the spread of smoke during a fire. By preventing smoke from permeating the entire structure, it offers a clear evacuation path for occupants and restricts further damage to the building interiors.

Controlling Smoke through Building Pressurisation

The principal strategy for restricting smoke dispersion involves generating air pressure differentials within designated smoke control zones. At its core, building pressurisation works by cultivating a higher pressure in the areas neighbouring the smoke zone. Consequently, air flows from these adjoining regions into the smoke-filled zone, effectively inhibiting smoke from spreading throughout the structure.

Understanding Dedicated and Non-Dedicated Smoke Control Systems

Smoke control systems fall into two main categories: dedicated and non-dedicated. A dedicated smoke control system, as the name implies, is solely designed for managing smoke dispersion. This independent setup, comprising air movement and distribution equipment, is not active under standard building operations. It’s employed for specialised areas like elevator shafts and stair towers, which necessitate specific smoke management measures.

On the other hand, non-dedicated smoke control systems are integrated with existing structures like the building automation or HVAC (Heating, Ventilation and Air Conditioning) systems. Upon activation, these systems shift their operational mode to meet the specific objectives of smoke control.

Distinguishing Between Fire Control and Smoke Control Systems

The primary objective of a fire control system is to quickly contain and extinguish a fire. Activated by the fire’s heat, these systems chiefly suppress the flames, not the smoke, relying on a water-based source such as sprinklers.

Conversely, smoke control systems are predominantly electrical, using fans and dampers to manipulate smoke movement. These two systems are usually distinct given their differing goals but should be designed to work synergistically, without disrupting each other’s functionalities.

For instance, if a building has a sprinkler system, the associated smoke control system doesn’t need to manage large amounts of smoke, as the fire’s scale should be relatively contained.

Furthermore, coordination is crucial when a smoke control system interacts with a gas-based fire extinguisher. If a smoke control system attempted to vent an area where a gas-based extinguisher had been activated, it could unintentionally vent the fire-suppressing gas, allowing the fire to persist. As a result, such systems shouldn’t operate simultaneously in the same section.

The smoke control system receives vital information about the fire’s location from a fire panel, which uses a combination of smoke and heat sensors. If signals from multiple smoke zones are detected, the smoke control system should continue automated operation based on the initial signal received.

Basic Types of Building Smoke Control Systems

Smoke control systems found in buildings typically fall into two main types: shaft protection and floor protection. Shaft protection includes stairwell pressurisation systems and elevator hoist-way systems. Conversely, floor protection entails various forms of zoned smoke control. Refer to the ABCB – Australian Building Codes Board’s “Restricting the Spread of Smoke Within Building Through Zone Pressurisation” The selection of a specific system, or a combination thereof, hinges on the building and fire code requirements, along with the distinct occupancy and life safety needs of the scenario under consideration.

Note:

Modern trends indicate that many buildings are being designed with refuge areas as required by the Disability Discrimination Act of 1992 (DDA). These refuge zones—usually situated next to stairwells or elevator hoist-ways—may necessitate special pressure compensation systems to sustain a habitable environment. The smoke control system’s designer must define the requirements for these systems, considering the smoke control system design and the related operational sequence. Encountering these types of zones might necessitate additional time and resources to ensure and confirm regulatory compliance.

Shaft Protection Systems

Shaft protection systems can be categorised into two types:

  1. Stairwell Pressurisation Systems

  2. Elevator Smoke Control

Stairwell Pressurisation Systems

Stair towers, equipped with a ventilation system and isolated from the main building, serve as the most common type of dedicated smoke control system. Fire-rated doors on each floor establish the only connection between the tower and the building. Ensuring a smoke-free stair tower is crucial during an evacuation, as occupants must use it to exit the building.

Pressurised stairwells aim to maintain a tenable environment, allowing occupants to safely exit the building. A tenable environment restricts combustion products, such as toxic gases, particulates, and heat, to minimise the impact on occupants. The secondary objective of stairwell pressurisation is to create a staging area for firefighters. This can be accomplished by mechanically pressurising the stair shafts relative to the fire area with outdoor air, preventing smoke contamination.

Stairwell systems are divided into two types:

  1. Non-compensated – A fan supplies air to the stairwell, providing two or more positive pressure differentials: one with all doors closed, another with one door open, and so on.
  2. Compensated – Similar to non-compensated systems, a fan supplies air to the stairwell; however, adjustments are made to the pressure differential based on various combinations of open and closed doors. This can be achieved by changing supply airflows or relieving excess pressure from the stairwell. Over-pressure relief may involve barometric dampers,(barometric damper is commonly used to relieve built up pressure in zoned duct system that could potentially cause damage to HVAC equipment) motor-operated dampers, an automatically opening stairwell door at ground level, or an exhaust fan.

It’s essential to pressurise a stair tower enough to keep smoke out. However, excessive pressure can make opening the door leading into the stair tower difficult.

stairwell pressurisation systems

Image source:  Schneider Electric

Controlling Smoke in Elevators

Elevator shafts pose a unique challenge for smoke control. Due to their design, they can serve as chimneys, drawing smoke up into higher levels of the building. Factor in the often deficient seals on elevator doors and the multiple openings on each floor, and you have a conduit for smoke dissemination throughout the building.

To make an elevator operational during a smoke emergency, it’s necessary to pressurise the shafts, similar to the process in stair towers. This, however, comes with complications. While one can improve elevator door seals and install rubber sweeps, these measures aren’t foolproof in eliminating air leakage. Besides, many elevator shafts aren’t built to withstand pressurisation, and the elevator cars themselves can cause localised pressure differences as they move up and down. Because shafts are often made of porous material, they may not be able to contain the air pressure. Additionally, inspecting and repairing cracks that could let in smoke or let out pressure can be challenging, as shafts aren’t designed for post-installation inspection.

While various solutions for elevator pressurisation problems have been suggested and explored, there are currently no definitive guidelines for smoke control in elevators. For more detailed information on potential methodologies and standards, please refer to NFPA 92 (NFPA 92 covers all types of systems used to address the impact of smoke from fire, with mandatory provisions for the design, installation, and testing of both new and retrofitted smoke control systems in buildings—including openings and leakage through egress doors in stairways) and UL864 (UL864 is the Standard for Control Units and Accessories for Fire Alarm Systems, governing the fire protection industry worldwide, with the most recent ninth edition revised in 2008) documentation. Note that local Authority Having Jurisdiction (AHJ) and specific project specifications may demand smoke control measures exceeding those detailed in the aforementioned standards.

Zoned Smoke Control for Floor Protection

While pressurised stairwells are designed to prevent smoke infiltration, buildings relying solely on these systems may still experience smoke spreading through floor gaps, partitions, and other shafts. This can endanger lives and damage property in areas far from the fire.

To address this issue, implementing zoned smoke control is crucial. This approach aims to restrict smoke movement within a building, offering greater protection and containment.

Implementing Zoned Smoke Control

Zoned smoke control restricts smoke movement within a building by segmenting it into separate zones, known as smoke control zones. These zones are delimited by smoke barriers such as partitions, floors, or closable doors.

Should a fire break out, it’s confined to its originating zone, now referred to as the smoke zone. Using pressure variations and air currents created by mechanical fans and operational dampers, the smoke can be restrained to this smoke zone. In response to a fire/smoke situation, all smoke control zones adjoining the smoke zone get positively pressurized while the smoke zone itself is negatively pressurized. Optionally, all other smoke control zones in the building could also be positively pressurized.

With the smoke zone isolated, the smoke within can then be vented. Typically, a UL 864 Listed Fire Alarm Control Unit or a protective signaling system (UOJZ, for instance) triggers the commencement of the zoned smoke control sequence upon receiving fire/smoke signals.

Smoke Control System Activation

The HVAC system’s operating controls must be designed or modified to prioritise smoke control mode above all other modes. Although smoke control sequences typically activate automatically, manual activation may be appropriate in certain cases. Regardless, the smoke control system must allow for manual override and deactivation.

Automatic activation of the smoke control system occurs when receiving signals from specific fire detection devices, or a combination of such devices. These devices include automatic detectors such as smoke detectors, waterflow switches, and heat detectors. Manual fire alarm pull stations are generally discouraged for activating automatic smoke control systems, except for stairwell pressurisation systems. This is due to the possibility of someone triggering an alarm from a location outside the originating smoke zone.

To Finish Up

Understanding the fundamentals of Smoke Control Systems is a step towards ensuring your safety and the preservation of property during a fire. These systems play a critical role in managing smoke movement within a structure, potentially saving lives and limiting damage during an unexpected event.

As we’ve learned, controlling smoke isn’t just about having exhausts or vents. It’s about strategically designing and implementing smoke zones, efficient barrier systems, and appropriate response times. By leveraging technology, we can optimise our response to these potentially catastrophic events, enhancing safety, and minimising overall impact.

At Complete Fire and Pumps, your safety is our utmost priority. With comprehensive knowledge and hands-on experience, our team is equipped to help you fully utilise and understand the intricacies of a Smoke Control System. We don’t just build and install these systems, we build safer environments.

Thank you for taking the time to read about the basics of Smoke Control Systems. Remember, stay informed and stay safe!

Best regards,

Alex and the Team at Complete Fire and Pumps

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