Smoke Control Design Principles for Warehouses and Single-Storey Buildings

When a fire breaks out, the consequences can be devastating. In warehouses or other large, single-storey buildings such as factories, not only are lives put at risk, but large quantities of stock can be destroyed as well. Depending on the damage caused, days or months of production time can be lost – a challenge that most companies might find it difficult to recover from.

In this blog, we aim to give you some more information about how a smoke control and smoke clearance system can help to reduce damage to buildings and stock, whilst keeping occupants safe.

How smoke control systems keep people, stock and buildings safe

When a building has an effective smoke control system installed, occupants are provided with a clear, breathable escape path, permitting them to exit the building far more quickly and safely. As well as aiding safe evacuation from a building, smoke control can assist fire fighters with entering the building safely, allowing them to move quickly through the area with improved visibility and an improved air supply. The time they save in finding the source of the fire also greatly improves their chances of putting the fire out before it becomes an uncontrollable blaze that could threaten the integrity of the building and destroy anything in it. For all these reasons, the type of smoke control system you choose to install in your building should be considered a long-term investment.

How does smoke behave when a fire breaks out in a single-storey building?

Before we explore the basic design principles involved in smoke control design for warehouses and other single-storey buildings, let’s look at the challenges a system would have to overcome.

The early stages of a fire:

When a fire starts in a large building, for instance a warehouse, it is not like a fire at home. If a fire started at home all the doors and windows could be closed to cause the fire to be suffocated and reduce rapid growth. In a large industrial building, the amount of oxygen available and the amount of air infiltration will mean that this would not be effective. The fire cannot be sealed off. In the early stages, smoke from the fire will quickly rise into the roof space.

Smoke characteristics:

The smoke can spread laterally at a velocity of up to 5m/s. An average person will walk at 1-2m/s and run at 7.5m/s. Once the building roof space is full, the smoke will start to build down. The rate at which this occurs varies significantly with the nature of the combustibles and building geometry

Smoke logging:

In an unventilated situation, a building with a volume of 10,000m3 can become smoke logged in just a few minutes. This was proven at the Colt test facility in Ghent (with a volume of 13,000m3) where it was shown that the test building became completely smoke logged in under two minutes. Although the smoke is made up mainly of entrained air, it can contain sufficient toxic substances and asphyxiates to disorientate and disable within seconds and kill within minutes.

The Basic Design Principle for Smoke Control in Single-Storey Buildings:

The basic principle of smoke control is to limit the spread of smoke through the building and provide a means by which the smoke and heat can be extracted. To achieve this requires three elements:

1. Openings or fans at high level to exhaust the smoke from the building.
2. Barriers to restrict the spread of smoke through the building.
3. Inlet ventilators to provide a replacement air supply to balance the smoke being extracted.

Considerations for designing smoke ventilation systems into single-storey buildings:

All the factors listed below need to be taken into consideration when designing a smoke control system for single storey buildings:

• Design fire size
• Steady state, or growing fires
• Ceiling jet
• Heat output of fire
• Clear layer required
• Smoke zones
• The effects of sprinklers
• Wind effects
• Air inlets / replacement air
• Depth of smoke layer
• Ambient temperature
• Plug-holing

The base dimensions of the largest fire which a smoke ventilation system should be expected to cope with should be worked out. Calculations are based on either a steady state or a growing fire.

Steady state fires

This scheme design is based on the anticipated largest fire size within the building, and therefore the smoke control scheme will be capable of accommodating any fire up to that size.

Growing fires

This scheme design is based on a fire changing size over a period of time depending on the contents of the building.

Ceiling jet

This is a ceiling fan that facilitates the horizontal flowing of hot gases driven in part by the kinetic energy of the rising fire plume. It typically has a depth of approximately one tenth of the building height.

Heat output

This is the total heat generated by the fire source. The convective element of this heat output drives the smoke flow.

Clear layer

The “clear layer” is the height from the floor of the smoke-free area that the smoke control system will guarantee if a fire broke out. The minimum clear layer for industrial buildings should be 3 m. The clear layer depth is very important as it permits the escape of personnel and the entry of firefighters.

Smoke zones

Where the building is considered too large it must be divided into separate zones by use of smoke barriers. Smoke zones should not exceed 2000 m2 if naturally ventilated and 2600 m2 if mechanically ventilated in plan area.

Smoke control design is a complicated science and each building will have different requirements and issues that need to be taken into consideration. If you are working on a single-storey project, get in touch with our experts for a free consultation. Our designers can help you throughout the entire process and ensure your building is safe and compliant at all times – contact us today.