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Home » Smoke exhaust – it’s serious: Active and static smoke barriers

Smoke exhaust – it’s serious: Active and static smoke barriers

By Ron Burns

Looking at the difference between active and static smoke barriers is always interesting.

When this edition hits the shelves, FRIGAIR 2018 will be only days away from launching. The hustle and bustle in the industry will be reaching new heights and there will be butterflies in many an exhibitor’s tummy as they prepare for this industry showcase. I will be presenting a paper “Smoke barriers — why they are critical, and EN 12101:1”, and I am looking forward to some discussions on the topic. I am aware that a stand will be dedicated to smoke and fire curtains for those industry participants interested in a touch and feel experience. The code refers to smoke barriers, with the texture of the fabric similar to internal curtaining. The general industry term for these components is ‘curtains’. In this article, the terms ‘barrier’ and ‘curtain’ are interchangeable.

Understanding what makes active and static smoke barriers different, is a good starting point. It would be safe to say that architects do not enjoy the striking visual appearance of a matt grey fabric sheet running through their meticulously designed mall space. Nothing cuts deeper to the core of aesthetic disaster than a 1 500g/m2 matt grey vertical fabric sheet suspended from the rafters. In buildings where care has been taken to fit crafted ceilings and coordinated fixtures, a static barrier definitely does not lend itself to receiving many compliments. Static barriers serve their purpose in a warehouse. Product is shipped and stored in brown labeled boxes and, most importantly, there are no customers, clients, shoppers, business professionals, or any members of the public. In that environment, the static smoke barrier is indeed a thing of beauty.

“It is important that the system designer, when calculating for a specific installation, takes containment efficiency into consideration.”

To those from the fairest Cape … A shopping centre named Blue Route Mall has several active smoke barriers installed in the general mall areas. It features long spans in excess of 35m of continuous active smoke barriers. The mall is complete with undulating ceiling features that house active smoke barriers. If you are fortunate enough to be in the mall during a fire drill, among the blaring alarms, you will see the active smoke barriers gracefully descending. Once they reach their design level, they stop, and the smoke fans initiate their start-up sequence. The barriers quiver in the breeze created by the extraction system. The routine test is successful, the drill is complete, and the barriers retract back into the ceiling void. The internal finishes remain intact in their full aesthetic splendour. The versatility of the products speaks for themselves.

From a functionality perspective, both products are identical and undergo the same performance testing criteria. The designer cannot for one moment imagine there is less engineering and care taken in the installation of either product. In fact, the installation requirements for the static barrier are far more stringent than those of the active barrier.

The code defines the difference between static and active smoke barriers as follows:

4.2.2    Static smoke barriers (SSB)
Static smoke barriers shall be fixed in their fire operational position at all times and according to their design classification.

Further on …:

4.2.3    Active smoke barriers (ASB)
Active smoke barriers shall move to the fire operational position upon external initiation and according to their design classification. Active smoke barriers shall be defined according to their application e.g. life safety protection or property protection, method of operation and external initiations.

[EN 12101-1 2005 Pg 11]

Active smoke barriers are further classified into four additional segments, which we will cover under another title. Active smoke barriers may either rely on gravity to descend to their design height or be powered to the design height. Should the designer elect to implement the powered option, it will be a requirement to ensure that the electrical reticulation to the active smoke barrier is fire rated.

Performance and classification

 Classification  Temperature (°C)  Time (min)
D 30 600 30
D 60 600 60
D 90 600 90
D 120 600 120
DA 600 Actual time reached above 120

Barriers are classified in D 30 or DH 30. D 30 barriers are tested at a constant temperature of 600°C for the specified time, in this case 30 minutes. In the case of DH 30, the DH refers to the testing of the smoke barriers in accordance with the standard heating curve (EN 1363-1) for the specified period. I have never had a requirement to detract from the standard 600°C temperature and time standard and cannot offer an opinion on the DH certification application.

As part of the reliability and durability of the static smoke barriers, it is a requirement that the manufacturer/supplier provides verification that the material used in the smoke barrier is fit for purpose. The material needs to be checked for tear strength, breaking loads, resistance to flexing, and flexural strength valid for the application.

“As part of the reliability and durability of the static smoke barriers, it is a requirement that the manufacturer/supplier provides verification that the material used in the smoke barrier is fit for purpose.”

When working with static smoke barriers, it has been my experience that the manufacturing process for the heat-resistant woven yarn makes it brittle. Premature installation into an unsealed building, which allows unabated wind paths in the building, can result in severe tearing and destruction of the smoke barrier fabric. This is an expensive error to make during the installation process. Care should be taken to ensure that the building is wind resistant and ready for the installation of the smoke barrier to avoid unnecessary damage to the fabric. Handling of the material requires diligent care and attention, as the fabric is sensitive to excessive handling. The woven yarns have a maximum leakage rate of 25m3/h/m2 at 25Pa at ambient temperature or 200°C.

The installation requirements of a certified static smoke barrier require meticulous attention to detail once all the components are delivered to site. Unlike the active barrier, the static curtain is assembled on site. Building site conditions contain many challenges not experienced when assembling an active smoke barrier in a manufacturing environment. The challenges experienced with static smoke barriers require additional care and caution while working at heights up to and including 20m above finished floor level. There are access challenges, and limited installation staff at the workface.

The completed smoke barrier requires accurate work at high levels and normally uses cherry picker access. The joining of the fabric requires stitched and seamed fixing of the individually supplied tailored fabric drops. These fabric drops are secured and fastened in a predetermined sequence while being positively fixed onto trusses. This is far more difficult than the installation of an active barrier that undergoes the same scrutiny and attention to detail on the workshop bench. Each smoke barrier type has its own unique set of challenges. However, the labour intensity and arduous working conditions on site, in my opinion, make the installation of the static smoke curtain far more challenging.

The designer has several challenges to overcome when selecting and specifying smoke barriers, whether static or active. Gaps are permissible. It is not a requirement to provide an airtight smoke barrier installation. The smoke barrier may require operational tolerances, as an example, crossing an expansion joint or traveling around a corner. It is important that the system designer, when calculating for a specific installation, takes containment efficiency into consideration.

Positioning of active barriers against walls often results in slight gaps along the perimeter, which are a result of the construction methods and concealed beams found in the ceiling voids. It is important to consider the positioning of the barrier in a concealed void, service coordination, and vertical positioning of the barrier. At times, the barrier may not practically be installed hard under the soffit of the slab over. In these instances, the space above the barrier requires sealing with a suitable material to maintain the classification achieved by the smoke barrier.

Although leakage gaps are permissible, these two examples of a smoke barrier installation are definitely to be avoided. Image supplied

Although leakage gaps are permissible, these two examples of a smoke barrier installation are definitely to be avoided. Image supplied

The following comments are made in the EN 12101:1 code and require no explanation. I include them for completeness when considering the installation of smoke barriers.

7 Installation

The smoke barrier installation shall comply with the requirements of prCEN/TR 12101-4.

The supplier shall provide appropriate installation information, which shall include the following:

  1. fixing component information;
  2. power requirements and connections (active smoke barriers only);
  3. installation instructions including perimeter requirements where applicable;
  4. commissioning procedure;
  5. operating instruction (active smoke barriers only);
  6. warnings to avoid obstructions to operation (active smoke barrier only);
  7. penetrations (static only);
  8. operating instructions, with maximum operating and loading tolerance for the product, e.g. maximum barrier weight, bottom bar weights, minimum/maximum motor speeds, overlapping and conjoining, and fixing methods.

NOTE: Care should be taken to ensure that the operation of an active smoke barrier is not obstructed, e.g.by cosmetic finishes, lighting, shelving, sales displays or racking.

[EN 12101-1 2005 Pg 26]

Maintenance of smoke barriers is important. The largest threat to life in any smoke ventilation system is cool smoke. Once the smoke has lost its buoyancy, extraction is extremely difficult. Maintenance is possibly the largest enemy of the smoke ventilation systems installed in buildings in South Africa. The following portion of the codes specifically addresses maintenance. Again, the following comments require no explanation.

8 Maintenance

In order to ensure continued compliance, reliability and integrity, smoke barriers shall be inspected, serviced and tested as defined in prCEN/TR 12101-4 by personnel trained and qualified in the product.

The supplier shall provide maintenance and testing information, which shall include the following:

  1. inspection and maintenance procedure;
  2. recommended procedures for operational checks;
  3. recommended check for obstructions to operation, e.g. by cosmetic finishes, lighting, shelving, sales displays or racking;
  4. recommended check for the effects of corrosion, etc;
  5. recommended check for mechanical fastenings;
  6. recommended check for power supplies and controls;
  7. recommended check for penetrations, holes, etc;
  8. recommended check for anything which materially affects the performance of the product.

[EN 12101-1 2005 Pg 27]

Part 5 defines channeling screens as:

3.1.10 Channeling screen

Smoke barrier installed beneath a balcony or projecting canopy to direct the flow of smoke and hot gases from a room opening to the spill edge.

[prCEN/TR 12101-5 2006 Pg 10]

Channeling screens provide the designer with many cost-saving opportunities in a smoke and heat exhaust ventilation systems (SHEVS) system. As mentioned, I will be presenting a paper at FRIGAIR on smoke barriers and why they are critical, looking at the EN 12101:1 standard. The normal life safety issues will be highlighted, adding perspective to the importance of smoke ventilation. Channeling screens will be addressed, and participants will be able to reflect on possibilities to limit the size of extraction volumes, including plant and space requirements, which are achievable by the introduction of channeling screens.

The presentation will take place on Wednesday, 6 June at 12:00 at the Gallagher Convention Centre in Midrand.

Ron Burns - Bio