"Cheap is not always cheerful"
In recent
surveys of car park ventilation systems, some alarming shortcomings have been
brought to light, particularly regarding the application of jet fan systems. There
are a range of inadequacies ranging from basic poor design where substantial
areas of the car park are devoid of ventilation by schemes originally designed
to ventilate and control smoke but in reality are incapable of achieving this
objective.
Jet fan
systems have been around for several years and with over 95% of new
installations being jet fan systems, people feel that it cannot be overly
difficult to design these systems themselves and simply purchase the fans. Even
systems designed and installed by some so called specialists however have
revealed substantial shortcomings.
Simple
misunderstanding of regulations and lack of knowledge of fan installations help
explain how many of these problems arise. A recent investigation on one
installation revealed two axial main extract fans installed in parallel,
discharging into a common plenum. Whilst this was correct, they were also
installed without non-return dampers fitted to the fans. This would mean should
one of the installed fans fail, there would not only be a loss of performance
in that fan but also a substantial reduction in the overall performance of the second
fan caused by air short-circuiting through the failed fan.
There have
been scenarios where the fire strategy has been accidently or purposely
disregarded. Another example was an installation where the fire strategy
required an advanced smoke control systems which could ensure that access to
lobbies were kept free from smoke contamination in the occurrence of a fire in
the car park. The reality was far from the requirements, with the most basic of
smoke clearance systems being installed, no meeting the requirements at all.
The most worrying aspect of this case is that between the consulting engineer,
the building control officer and the client, none picked up on this and instead
only recently was it identified by a fire officer and thus we were called in.
Why does
this occur? The main motive is cost and the "design & build"
culture in which the original objectives created by the architect, consulting
engineer and fire engineer become lost, disregarded or forgotten against the
background of Value Engineering.
This is not
to say there is anything wrong with Value Engineering if the original objectives
and strategy are met; however these can be easily forgotten and conveniently ignored
when the contractor, encouraged and guided by a fervent pseudo-specialist who
promises wonderful cost savings. When told by a specialist that the system will
be “fully code compliant” and will meet all building regulations, it becomes
very plausible and it may very well be the case. Conversely what has been
overlooked is the initial enhanced design specification that was agreed at the opening
design stage and against which relaxations were granted by building control on
the requirement for sprinklers and the ventilation of access lobbies.
This can
result in a range of problems. It could be several months later that the error
may be identified. This leads to an expensive process of correcting the
mistake, therefore rendering the once wonderful savings pointless as the
initial savings become a drop in the ocean compared to costs of correction.
Most importantly, not only could the handover of the building be delayed but if
these shortcomings are not ultimately identified, the occupants and residents
of the building could be put at considerable risk.
So how can
we prevent this in the future? Through a fundamental understanding of how the
original system design was developed and why. If apparent savings offered by
alternative suppliers of specialists systems appear too good to be true, then the
chances are they are and discussions with the companies involved in developing
the original design should always be consulted in order to gain a full
appreciation of the design requirements and objectives that must be obtained.
Richard
Brooks
Richard
Brooks is General Manager of the Advanced Smoke Group with over 35 years
experience in the smoke control industry. He was Chairman of the Smoke Control
Association 2002 – 2004; Chairman of the Association’s working group on the guide
to the Ventilation of Loading Bays, Service Yards and Coach Parks; a member of
the British Standards Institute Fire Engineering Group (FSH25) and a member of
the BSI working group, drafting BS7346: Part 7: 2006 for Car Park Ventilation.
