Pyro Mi cables successfully witness tested to the stringent fire
test methodology of BS7346-6:2005
Tyco Thermal Controls has led the way by example in
having its Pyro MI mineral-insulated cables undergo
Lloyds Register witness testing under the new, more
stringent, fire test methodology of BS 7346-6:2005. This
cable successfully achieved the highest performance
requirement of 120 minutes survival time for fire
fighting systems. The Standard applies to cables above a
notional size of 20mmØ, but also recognises smaller
cables that can be accommodated in the test rig. As many
MI cable sizes typically used for life safety and fire
fighting circuits are significantly smaller and lighter
than other cables of an equivalent rating in the
Standard, Tyco Thermal Controls also took the
opportunity to subject Pyro MI cables down to12mmØ to
the same rigorous tests and were able to demonstrate
that these too will meet the highest fire performance
requirements.
BS 7346-6:2005 is the recently introduced Standard for
fire-rated cable systems, defining the performance
requirements of various types of fire-rated cables (up
to 600/1000V) in maintaining circuit integrity for life
safety, fire-fighting and property protection systems
under fire conditions.
With the introduction of BS7346 in respect of fire-rated
components, and specifically in Part 6 - Specification
for cable systems, the British Standards Institute
addressed the long standing concerns with respect to
fire test methodology.
These had been earlier recognised in the commentary to
BS 5839-1:2002, for fire alarm cables that identified a
need for revision of the test methods of BS 6387 (for
which the test rig is limited to smaller cables up to
approx 20mmØ) to more accurately replicate the physics
of a real fire scenario.
BS 7346-6:2005 introduces new test methods to assess
cable performance under conditions of direct application
of fire, direct mechanical impact and fire-fighting
water shock – all conditions associated with a real fire
incident. Where previously each element of a test was
conducted on a separate cable sample, this Standard
requires the complete test to be applied to a single
cable sample and, for the first time, it is subjected to
direct mechanical shock and water jet impacts.
The test methodology has been devised, for a single
cable sample, to validate that the fire-rated cable will
maintain circuit integrity for the required survival
time whilst simultaneously:
• withstanding a constant temperature attack at 842°C
• withstanding repeated direct impact shock of approx
10N at 10 minute intervals.
• withstanding direct water jet impact equivalent to a 2
bar water hose at the point of mechanical impact during
the last 5 minutes of the required survival time.
The BS 7346-6 Standard describes two classes of system,
Life Safety and Fire Fighting which, when applied,
determine the appropriate performance requirement
according to the function of each circuit.
Life Safety requires control systems to remain
functional for alarm and to support evacuation.
Suggested survival time requirements assessed as being
for instance 30 minutes for single stage evacuation or
60 minutes for multi-stage evacuation.
Fire fighting systems require circuit integrity for 120
minutes to serve active systems for protecting and
assisting fire-fighters in carrying out their role and
would typically include pressure differential systems
for fire-fighting, smoke and heat exhaust ventilation,
sprinklers and fire fighting lifts.
Contained in the Standard are a table and an annex which
provide a matrix of suggested survival times to meet
different fire performance objectives. Obviously, if for
practical reasons a single cable type is to be employed
for all applications then it would need to have the
maximum fire survival performance to maintain full
system integrity.
Most active fire safety systems in buildings rely on a
dependable electrical power supply for detection,
alarms, evacuation and communication thereby enabling
safe evacuation and assisting the fire fighting
response. In the event of fire it is critical for
electrical circuit integrity, for power, signal &
control, to sustain operation systems incorporating
equipment such as, sprinkler pumps, shutters and smoke
curtains, smoke ventilation systems, fire fighting
lifts, smoke control dampers and pressurisation fans.
The electric cables which maintain power, control and
signals to such equipment are fundamental to the task.
By introducing a more accurate replication of fire
dynamics into cable test methodology and classifying
objectives, BS 7346-6 offers fire safety engineers a
meaningful guide to the capability of different fire
performance cables in respect of their application.
Within the new Standard, building services engineers and
fire engineers, responsible for specifying fire-rated
cable systems into ever more complex buildings, are
provided with clear guidance for the selection of
appropriate fire-rated cables to support Life Safety and
Fire Fighting applications.
Email:
SalesUK@tycothermal.com
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