Active vs. Passive fire
safety systems
Presented by Rob Taylor
UNFORTUNATELY THE MONT BLONC TUNNEL FIRE
24 MARCH 1999 WAS NOT A HOT SMOKE TEST
“Smoke fans 'fed Mont Blanc fire'
Reversed extractor fans caused Mont Blanc fire deaths, says
report
A DECISION to reverse smoke extractors inside the Mont Blanc tunnel
soon after fire broke out contributed to the intensity of the blaze which
killed 41 people, according to the preliminary report on the disaster
published on Tuesday.
As a result of the decision fresh air was sucked into the tunnel through
the ventilation system at the Italian end, fanning the flames and
spreading the fire.”
Manslaughter convictions follow
Mont Blanc fire
ACTIVE SYSTEMS CAN MANAGE SMOKE EFFECTIVELY - BUT WE
MUST TAKE MEASURES TO LIMIT THE POTENTIAL FOR OUR
ACTIVE DESIGN SOLUTIONS CONTRIBUTING TO A FIRE
DISASTER –assessments consider RWCFS and sometimes RS
Fire Engineering Professionals
Rob Taylor - Active vs. passive fire safety
systems and their merits for application within
engineered buildings
The following information is the opinion of the speaker, and may not be considered factual.
Bullying example
Remain in a group of
friends all the time to avoid
confrontation?
OR
Learn self defence?
Passive
Active
Home Security example
High security fence?
OR
Shotgun?
Passive
Active
Fire Engineering is no different
As fire safety engineers things are no
different
Almost all alternative solutions need to
consider active and passive approaches.
How can a fire engineer decide which
approach is more suitable- what are the
driving forces?
Fire Engineered Designs
Engineered designs are to a large extent
driven by:
Shackles of BCA DTS provisions; and
Architects desires to break these shackles
and work outside the DTS provisions
Architects often prefer to replace passive fire
safety systems with active systems
Improves flexibility and client focus
Active / passive system considerations
When would an active system provide better
performance/reliability to a passive system?
Which applications are best suited for an
active approach and which to a passive
approach?
To help us choose between active and passive
solutions we can consider examples where
passive and active approaches perform
and examples where they perform poorly
Sole Occupancy Unit (considered to be
example of good passive design )
Fire rated bounding construction within a
residential Sole Occupancy Unit
Required for: Fire safety, acoustic isolation,
security and privacy
An active solution for the same example
would be unlikely to prevent fire spread as
effectively
A hole in the wall is likely to be repaired
quickly; whereas an active fire safety system
may remain un repaired for some time
Large Shopping Centre example
(considered to be example of poor passive design )
Inappropriate use of bounding construction in
a large 2 level shopping centre, divided into
2,000m2 fire compartments
This example would not require:
Sprinkler systems
Smoke exhaust
Smoke detection in some areas
Vehicular access
Cont’d
Large Shopping Centre example
It would, however, require the following
passive fire safety systems:
Fire rated walls bounding tenancies
Sliding fire doors or fire shutters separating
mal areas
Sliding fire doors require high maintenance
are against current best practise, as they
block occupant exit paths
Cont’d
Large Shopping Centre example
Installing active systems such as:
Sprinkler protection
Smoke exhaust
Smoke detectors
would be expected to increase the building’s
fire safety
Sprinkler protected single tenant large warehouse
example (considered to be example of good active design )
Warehouse provided with automatic sprinkler protection in
lieu of multiple fire walls with extensive protected openings
Warehouse has brigade perimeter vehicular access.
Sprinkler system tends to be out of reach of fork trucks and
therefore tends not to be damaged. If damage occurs and a
sprinkler system is set off, this alerts then owner and an
immediate repair is likely to prevent flooding.
Plate glass window protected with Standard Response
sprinkler heads to prevent fire spread to required exit
travel path in lieu of fire rated passive construction
Plate glass windows are likely to break in the
event of a fire prior to sprinkler activation or
upon sprinkler activation Passive fire resisting construction would be
expected to be more effective and reliable
than the wetted glass option.
Active systems (opinion on reliability and
performance)
Sprinkler system
High reliability
High performance
Low potential for adverse impact
Smoke detection system
Medium reliability
Complex systems can have adverse impact
EWIS system
High reliability if regularly used by trained fire wardens
Minimal potential for adverse impact
Smoke exhaust
Reasonable reliability for simple systems
Poor reliability for complex systems, and increased potential for
adverse impact
Zone smoke control
Similar to smoke exhaust
Stair pressurisation
Reasonably reliable when correctly designed, limited potential for
adverse impact
Passive systems (opinion on reliability and
performance)
Wall/floor construction
High degree of reliability if required for multiple reasons
other than fire safety. ie: acoustics, privacy and security
Fire rated protection around structural elements
High degree of reliability if suitably designed and vice versa.
ie: unprotected lightweight construction in warehouse areas
may not afford a high degree of reliability whereas concrete
may
Self closing fire doors
Reliability heavily dependant on location and use
Smoke baffles
Can be reliable if in areas not subject to frequent change
Incipient ceilings
Low reliability if not well designed/managed
Hybrid systems (active + passive) (opinion
on reliability and performance)
Fire shutters
Difficult to maintain, can result in low reliability if used to
enable vehicle access
Can have adverse affects on occupant evacuation within
major thoroughfares
Magnetic hold-open sliding fire doors
Comments as for fire shutters
Wall wetting sprinklers
Can be effective in the right location if correctly designed in
accordance with a tested prototype system, otherwise can
be ineffective
Smoke curtains
As for fire shutters except can also be adversely affected by
pressure differentials
Summary
The most acceptable solutions must consider:
The ability of the design to achieve the necessary level of
performance
The reliability of the fire safety systems
The potential for adverse impact on fire safety
Low reliability systems may require multiple levels of redundancy to
achieve a desired outcome- If systems are thought to have low
reliability issues, then the FEB should address this through a
requirement for increased redundancy assessment
The most effective passive systems are where they are required for
other reasons (security, acoustic isolation and privacy)
Systems should be as simple as possible and designed to minimise the
potential for adverse impact
Regular testing and inspection by the FSE may help improve reliability
and help minimise potential for adverse impact.
Questions?
Thankyou
Images courtesy of Google images.