To motorise, or not to motorise

Belimo Automation FZE's Managing Director David Stevenson explains the importance of fit for purpose fire detection and prevention technology.

“Much more guidance is given on the activation of fire/smoke dampers by smoke detectors”

Fire spread through ductwork is generally considered to be mitigated against by the use of ductwork and fire dampers in compliance with various codes of practice. The codes recognise various qualities of dampers and their method of operation, but regulatory guidance states that all alternatives are equally acceptable. This leaves the customer to take up the cheapest option - such as the thermally operated fire curtain damper - for regulatory compliance. This is not an effective method of preventing the spread of cold or even warm smoke, and certainly would not always be 100 percent effective, even against the spread of hot smoke depending upon the efficiency of any thermal triggering device.

Contradictory guidance

A further potential conflict between the Regulatory Authority, whether Local Authority, Building Control Officer or the Risk Assessor, is the subject of maintenance, again because of wooliness in the guidance. The guides state that in 'dust laden' and similar atmospheres, the operation of the damper should be confirmed by testing at intervals suited to the degree of pollution. It has long been recognised that checking damper operations is more easily carried out with motorised actuators than with manual operation. The Risk Assessor will normally take frequency of checking into account and may well require an enhanced level of checking over and above that which is sensibly achieved by manually checking fusible link operated dampers. However, if again the minimum specification has been accepted by the Building Control Authorities, the Risk Assessors expectations may be deemed incompatible.

BS5588: Part 9 states that 'all fire dampers should be simple in their operation with the minimum number or moving parts'. In fire performance terms the code only requires the dampers to satisfy the integrity requirements of BS476: Part 20: 1987 and whilst it recognises the enhanced insulation that an intumescent damper can provide, and even acknowledges the existence of intumescent dampers with integral, detector operated smoke blades; the basic recommendation is for fusible link operated integrity only dampers. Such dampers are recognised as not generally being fully effective in resisting smoke, but it does state that the 'integrity only' damper will 'assist' in reducing or retarding the movement of smoke. Without qualification, such a statement could be seen as highly optimistic.

Much more guidance is given on the activation of fire/smoke dampers by smoke detectors. Indeed, there are positive advantages in life safety terms in actuating fire/smoke dampers by smoke detectors (in addition to) thermally activated devices, particularly in buildings presenting a high, or special life hazard such as hotels, hospitals and other non-domestic buildings involving a sleeping risk and entertainment premises as an example of a special risk.

Concerns

Codes of practice, such as, BS5588: Part 9, heavily promote the concept of dampers for isolating the duct between the separate compartments which handle the risk of fire spread. However, very little guidance is given on the specification, or performance of such. Dampers dividing compartments will invariably be fairly simple robust mechanical dampers that are operated by a fusible link if the regulatory guidance is followed. Such dampers do not react to smoke ingress into the duct until the smoke has a temperature sufficiently elevated to operate the fusible link. 

As a consequence, in a slowly developing fire, significant volumes of smoke can spread through this ductwork, potentially putting people at risk in remote positions before the damper has operated. The fact that dampers are not generally designed to provide smoke resistance is of a lesser concern than the fact that they will not operate early in the fire event. How can a damper be installed such that it does activate early enough to make a contribution to the control of smoke spread? The only sure way is to have the damper so that it operates from a smoke detector, preferably closing in a controlled manner using motorised actuators, fit for the purpose.

Belimo Automation FZE is located in Dubai Airport Free Zone, which serves the entire Middle East. It holds the full range of Air and Water products in stock. The Swiss based company has been manufacturing electric actuators for air dampers and valve technology in heating, ventilating and air-conditioning (HVAC) systems since 1975. Belimo has become a world leader in this specific market.