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Damper Release Mechanisms

Different words are often used to describe the method of actuation of Fire Dampers. Very often words such as Automatic and Manual are used. ‘Automatic’ is used to describe a damper that has an actuator, and ‘manual’ being used to describe a damper that is activated by a mechanical device such as a fusible link.

Mechanical release mechanisms typically utilise a material that either changes state (i.e. melts) or expands, due to the localised increase in temperature. This, combined with springs, cause the dampers to close. This type of actuation can be referred to as Mechanical.

A motorised release mechanism takes the form of an actuator that operates the damper blades. Due to the need to have fail safe operation (a mechanism that returns the damper to a closed, and therefore safe state), there is normally a spring within the actuator to provide the energy to achieve this. In industrial or tunnel Fire Dampers applications, due to the size of the damper, you may need a large actuator where a spring may not be able to provide enough energy to close the damper, and therefore they may use batteries or capacitors to provide the energy to close the damper. Motorised release mechanisms tend to be electric; but it is also possible to get pneumatic actuators as well.

In all cases the dampers must have their own method of activation when subjected to an increase in temperature, so all could be considered automatic in one sense. In the event of a fire, dampers that have an electrical actuator are designed to close and stay closed, until the fire alarm panel or damper panel is manually reset. To therefore avoid this potential confusion, these will be referred to with the terms ‘mechanical’ and ‘motorised’.

It is important to remember that the closure mechanism is NOT linked to the damper classification. Where the confusion comes in, is that historically in the UK, curtain style fire dampers that have a mechanical release would only have a E classification, and Fire Dampers that have a motorised release would have a ‘ES’ classification. Assumptions therefore get made that all ‘E’ classified dampers have a mechanical release, and all motorised dampers have a ‘ES’ classification. This is not the case. Dampers are available with E, ES, EI, EIS classifications and in many cases both methods of actuation are available. When comparing and selecting products, it is essential that the both the method of release and the damper classification meet both requirements of the project (for example, integration within a smoke or fire detection system) and building regulations. Some examples of guidance to meeting the requirements of building regulation can be found in the following:

BS 9999:2017 section
Method 4 may be used for extract ductwork passing through the enclosures of protected escape routes, both where the ductwork does and does not serve the escape route (Figure 32 is an example of where ductwork serves an escape route).

With Method 4 being defined as automatically actuated fire and smoke dampers triggered by smoke detectors.

Approved Document B Volume 2 Section 10.16:
“An ES classified fire and smoke damper which is activated by a suitable fire detection system (method 4) may also be used for protected escape routes”

A EIS classified damper would exceed the classification requirements as stated above, but if it only has a mechanical release, then it probably cannot be activated by a suitable control system and would therefore not be appropriate for meeting the requirement of method 4. A damper with the same classification but with a motorised release would considered to meet the requirements of method 4.

Dampers that have a mechanical release are more difficult to test and reset than motorised dampers. In the case of mechanical release mechanisms that are only resettable from inside the duct, you will need to gain access to the damper via an access door in the duct and insert your hand into the duct to the damper, release the dampers blades, and then reset them and the mechanism. This is generally done one handed, and by feel. This is made more difficult in some case by the poor positioning of access doors, or the incorrect use of TEK screws to join the ductwork to the damper. This not only presents a health and safety risk to the user, but also compromises the ductwork’s ability to break away from the damper in the event of a fire.

The problems described above means that people don’t test the dampers because they can’t, or its too difficult. The mandatory testing is therefore not taking place and in the event of a fire the likelihood of correct operation is reduced, potentially significantly.

Some manual dampers can be tested and reset externally without having to put your hand into the duct. This make things a little easier, however, you do still need to get access to the damper, which, depending on the location, could involve ladders or scaffolded towers.

Dampers with a motorised release mechanism are generally easier to test. When these dampers are tested remotely, the positional information that the panel is receiving is via limit switches from the actuator, not the damper. So whilst the panel is showing that the damper might be closed, there is no guarantee that the damper is closed. We would therefore recommend a full inspection of the damper as defined in BS9999:2017 or other relevant guidance documents regardless of how often they are cycle tested.

To sum up:
• There are two methods of activation, mechanical and motorised
• The method of activation is separate to the damper classification
• Mechanical dampers are more difficult to test then motorised dampers
• Dampers must be visually checked at appropriate frequency, even if they are connected to a control system