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Smoke control: Smoke control vs smoke clearance

Smoke control: Smoke control vs smoke clearance

By Ron Burns

Today we journey through misused language terms and explore the devastating effects of spelling errors and poor understanding of language.

A phrase I often use when drilling down into a host of verbal instructions is, “I can only be responsible for what I say, not what you hear.” Ensuring there is clear understanding when picking through any system designed to save lives, requires careful and unrushed planning. Making sure the building and its contents are also protected does not necessarily mean additional cost, but it does mean additional thought.

‘Radical transformation’ and other misused phrases: all that is required to provoke frustration, expectation, and anger is to add an adjective or other descriptor in front of the word ‘transformation’. Here are a few from a South African perspective to illustrate the point: ‘economic’, ‘political’, and ‘land’.

In our normal day-to-day business activities, we have all transformed from a Ø1 000 fan to a 1 200 × 1 200 duct; we may even have shortened the length of the transformation, ensuring we do not ‘waste’ sheet metal and save on cost. Occasionally, we may have offset the square to round a little during the process, or perhaps ‘squeezed’ the duct a little. At which point is the transformation deemed radical?

A vast difference exists between ‘squeezing a little’ and ‘radically transforming’. A duct transformation with an offset that finishes with the centre line of the fan dropping level to the bottom of the fan — that is radical. The impact of this fundamental error is no different to other ‘radical duct fittings’. A fan mounted directly to a fan plate and bolted directly to a bend, or a discharge louvre, radically impacts on the performance of the system. The principle may look acceptable to the average person; however, a student of air movement would immediately question the functionality of the system and quickly conclude that the performance of the system is going to be dramatically different to the designed outcome.

Smoke control systems are one of the most complicated and often misunderstood systems within a building. It is important to understand the objective when providing a smoke control solution and when the provision of a smoke clearance system may suffice. Too many discussions take place where the two terms ‘smoke control’ and ‘smoke clearance’ are interchanged without the necessary understanding of the difference in the principles.

My good friend Google was unable to provide sufficient insight, but I did find a few explanations that were largely slighted to selling a product. I found one definition that seemed close to providing a definition and which did not leave me feeling that I need to align with their products:

“Smoke control is an aspect of fire safety that refers to the principle of redirecting hazardous smoke and fumes in the instance of a building fire. A correctly working smoke control system will keep smoke away from escape routes and enable easier ingress for firefighting services, saving both lives and assets, which are otherwise at serious risk from smoke during a fire.”    [www.airvent.co.uk/what-is-smoke-control/]

There was no suitable definition on smoke clearance; even Wikipedia was not prepared to venture into this smoky topic. My definition will have to suffice; here goes: “Smoke clearance is the removal of smoke from a space within a building without maintaining a clear layer or facilitating escape.”.

This is fundamentally different from a smoke control system. A colleague currently working at Colt International, Ron Daiper, once made a statement during an educational presentation on smoke control, which has proved useful to me over the years when I have been analysing smoke extraction paths. It went something like this: “If you are relying on the smoke to find its own path to the extraction point, you have no control. If you want to extract the smoke from the space, control the movement of the smoke and control the path the smoke is going to take to get to the extraction point. Do not rely on the smoke behaving as you require, rather control the smoke behaviour.”

Picture in your mind the number of shopping malls where the smoke ventilates from a line shop under 800m2 into a mall where the smoke baffle does not align with the external wall of the shop. Where the smoke baffle is positioned along the shopfront and not the boundary wall of the shop. The smoke may exit the line shop and enter the mall, contaminating two smoke zones. We are not going to investigate the effects of that decision now. We can, however, point out that the designer now has two smoke zones to control, as opposed to a correctly positioned baffle and a single smoke zone to control.

In South Arica, smoke clearance is a generally accepted method of clearing smoke from a parking basement. I would like to explore the utilisation of a smoke clearance system for a warehouse — not the normal run-of-the-mill warehouse, but a warehouse with different occupational and usage requirements. A unique and complex building. (We will explore basements in a separate discussion.)


I wish to encourage exploration into different aspects of ensuring that lives will be saved and buildings are protected when planning fire protection systems.


A colleague had a refurbishment project that provided a few challenges. The warehouse was large: 15 000m2. The initial design left a lot to be desired — a system of vertical louvres, permanently open, and bird ingress addressed by the installation of plastic wire mesh screens. I wonder why keeping the birds out was more important to the original designer than getting the smoke out of the building? Vertical ventilation is non-existent in a head wind. In accordance with EN 12101, a wind with a velocity greater than 1m/s in the replacement air inlet path requires addressing. The first step was to blank off the vertical louvres. Thereafter, a set of simple calculations to determine the aerodynamic free area required for the installation of roof ventilators. Select the smoke zones and prepare the submission drawings. A relatively simple project, right? Unfortunately, this was not the case.

As a general rule of thumb, I have noticed, when I get offered a choice of coffee, flat white or cappuccino, some dark, smoky secret is lurking. I was not to be let down: the drawings were rolled out on the table and the building geometry explained. With a chuckle, I was informed that the vertical louvres were to be removed. As though magically synchronised, the coffee arrived. At this juncture, I was told that the client was from an international stable who, in their technical specification, required the installation of extra-fast response sprinklers. My colleague explained that the smoke control, although a requirement for installation, was not required for activation when the fire occurred. The requirement was for the sprinklers to douse the fire and prevent fire spread. The design would require additional escape points, early warning detection, and a voice-over evacuation system alerting employees to evacuate the building. The building was not open to the public and the occupants would conduct regular fire drills, ensuring all occupants could escape quickly should the need arise.

The requirement was for the building to be fitted with a smoke clearance system that would allow the fire department to operate the system when they arrived at the site. The concern of activation of the smoke extraction system was the presumed negative effect on the activation of the sprinkler system. According to my colleague, there is sufficient data to support the theory that early activation of the sprinkler would prevent development of the fire and allow for early extinguishing. Should the firefighters arrive and require smoke ventilation, the firefighters could initiate the smoke clearance system. We discussed a few scenarios and concluded that both high- and low-level extraction would best suit facilitating the smoke clearance option. The high-level fans would pick up any hot smoke that may exist in the building. A series of low-level extraction points would expel any cool smoke that had lost its buoyancy. The height of the building and the installation of high- and low-level fans would suffice. The requirement to include jet was deemed unnecessary.

The building was divided into eight smoke zones. Smoke curtains were not required as smoke control and quick smoke clearance were not a requirement. The building would be evacuated and the occupants would be safe. The smoke clearance system comprised two fans with an extraction rate of 14m3/s each per smoke zone. The replacement air inlets were selected in accordance with the EN 12101 requirements, limiting the velocity to 5m/s. The replacement air was installed in the perpendicular façade to the extraction points, adjacent to the access into the building. The thought process supporting this decision was to allow the smoke to clear from the access points that the firefighters would use when entering the building, should additional firefighting be required.

This method of dealing with a fire condition is the first project I have worked on where this principle was considered. Although this is an alternative to maintaining a clear layer in the building, the fire engineer was satisfied that sufficient steps had been taken to prevent any loss of life, limit fire spread, and allow firefighters the opportunity to enter the building in a ‘safe’ environment. The use of the extra-fast response sprinklers was critical to this view taken on the smoke clearance philosophy and would definitely not be considered for a warehouse fitted with standard response sprinklers. I wish to encourage exploration into different aspects of ensuring that lives will be saved and buildings are protected when planning fire protection systems.


Click below to read the November 2017 issue of RACA Journal

RACA Nov2017

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