Protecting high bay and canopy structures from fires
Iain Hoey
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By Ryan Fogelman, J.D., MBA, vice president of strategic partnerships for Fire Rover and James “Andy” Lynch, MSc, CEO of Fire Solutions Group
High bay and canopy structures pose unique challenges when it comes to fire protection.
These expansive spaces, often found in industrial settings, warehouses and outdoor canopies, require specialised fire suppression systems that can quickly and effectively detect and combat fires.
Traditional methods, such as sprinklers and beam detectors, face limitations in these environments, making it crucial to explore alternative solutions to properly protect these spaces.
Recognising this, we developed the patented Fire Rover Automatic Water Cannon (AWC), a fire protection technology designed to provide rapid detection, visual verification and targeted suppression, thereby reducing nuisance alarms and ensuring enhanced safety measures.
Challenges of fire protection in high bay and canopy structures
High bay and canopy structures are characterised by their towering ceilings, which can significantly delay the activation of conventional fire detection and suppression systems.
Sprinklers, for instance, rely on heat detection to trigger water release.
Still, the height of these ceilings often means the fire has significantly progressed by the time the sprinklers activate.
This delay can result in extensive damage and increased risk to personnel safety.
The activation time for a fire sprinkler in a high bay is significantly longer compared to the activation time for an optical flame detector (OFD).
OFDs use line-of-site detection methods and are tested to FM standards, typically at 100 feet with a small pan fire.
The fire size at detection for the OFDs is between 100 and 250 kilowatts (kW), while the fire size at detection for the overhead sprinkler in a high bay require the fire to grow to be over 40 times larger.
Picture a small campfire compared to a very large bonfire.
Moreover, in open-air environments like tall canopies, weather conditions such as wind pose additional complications.
The buoyant plume generated by a fire can be easily dispersed by wind, rendering traditional sprinkler systems ineffective.
Even moderate wind speeds can push the plume entirely out of the structure, activating the wrong sprinkler heads or failing to suppress the fire altogether.
Modelling sprinkler activation in windy conditions
For a recent project, modelling of the sprinkler activation of a high bay open structure was conducted using the National Institute of Standards and Technology’s Fire Dynamics Simulator (FDS), an open-source computational fluid dynamics package.
FDS utilises Large Eddy Simulation (LES) numerical solution approaches to model the dispersion of gases, specifically low-speed, thermally driven flows like those typically found in fire scenarios.
A Cartesian grid system is applied over which the solutions for thermal plume concentration with time can be solved.
Eight scenarios were modelled with varying fire sizes and structure openings.
A simple building mock-up was simulated to evaluate wind effects on a smoke plume in an open-walled building.
Four scenarios used two heat release rates (1 MW and 5 MW) and two rollup door configurations (one door and four doors).
The fire source was in the centre of the processing pit.
Wind was set at 14.5 mph entering the building’s open side and exiting through the rollup door(s), representing the average wind speed and prevailing direction in the area, per the National Oceanic and Atmospheric Administration.
The simulations used a coarse grid with a cell size of approximately 1.6 feet for a computational domain of 1,416,960 total grid cells and ran for at least 20 minutes.
The domain included an array of sprinklers above the fire with 10-foot spacing, an activation temperature of 135 degrees Fahrenheit, and a relative thermal index of 130.
The simulations varied fire size, door configuration, and wind speed.
Sprinkler activation occurred in all simulations without wind (0 mph), but only in one of the four simulations with wind.
The modelling was limited to steady-state fires and one wind speed and direction.
Despite these limitations, the modelling shows sprinkler activation can be compromised under average wind conditions.
This results in extremely fast sprinkler activation times.
In a similar scenario with the same door and fire scenario but incorporating an average wind condition, despite the extreme thermal condition, the wind can deflect the plume.
This effect would be even greater if a fire growth rate was incorporated into the model rather than the large steady state fire.
Images taken of scenario S2W-5MW, demonstrating the wind flow and smoke condition, respectively.
In this scenario, four doors are open, a 5 MW fire is present and a 14 mph wind condition is imposed on the structure.
It was seen that the wind is directed though the building, deflecting the plume and carrying the heat out of the structure.
Advantages of the Automatic Water Cannon
The Automatic Water Cannon (AWC) is ideal for addressing the challenges posed by high bay and canopy structures.
This state-of-the-art system integrates advanced technology to address the limitations of traditional fire protection methods, providing efficiency and effectiveness.
The AWC utilises thermal detection and flame detection to swiftly identify fire incidents within high bay and canopy environments.
This rapid detection ensures firefighting measures are initiated at the earliest possible stage, minimising the spread of flames and reducing the potential for extensive damage.
Once a fire is detected, the AWC deploys targeted suppression via a remotely controlled monitor, delivering water, foam or listed water additive agents directly to the source of the fire.
This targeted approach ensures maximum effectiveness in extinguishing flames while minimising water usage and collateral damage.
An FM Global report from April 2020 entitled “Reducing Water Demands with Innovative Fire Protection Solutions” showed that AWCs like Fire Rover reduced the water demand by up to 92% when compared to traditional sprinkler systems.
By integrating visual verification capabilities, the AWC distinguishes between actual fire events and false alarms, allowing for prompt and accurate response by firefighting personnel.
This not only enhances overall safety but also reduces operational disruptions and maintenance costs associated with false-alarm incidents.
This is done utilising certified UL Central Stations for monitoring, alarm verification, targeting and suppression activation.
High bay and canopy structures present unique challenges for fire protection, necessitating specialised solutions that can overcome the limitations of traditional methods.
The AWC represents the latest innovation in this regard, offering rapid detection, targeted suppression and visual verification capabilities specifically tailored for these environments.
With its ability to overcome the delays inherent in traditional fire protection systems and mitigate the impact of external factors such as wind, the AWC ensures enhanced safety and peace of mind for personnel operating within high bay and canopy structures.
By investing in advanced technologies like the AWC, organisations can effectively safeguard their assets, personnel and operations against the threat of fire, ensuring uninterrupted productivity and business continuity.
