Click on Fire Test thumbnails below for enlarged views
London Underground Limited have commissioned Chiltern International Fire (CIF) to provide a test protocol against which manufacturers of water mist systems can test their equipment for efficacy in fighting fires in escalators. The protocol is titled "Escalator Water Suppression System Standard LUL EWSS TS1" and CIF have constructed a purpose-built rig for carrying out the test fires. Details of the procedure are shown below.
The enclosure used
for the evaluation of water mist extinguishing systems is a purpose built
structure mounted at 30 degrees to the horizontal. The test rig is designed to
show one zone of an escalator with timber cribs used to represent the fire load
of a modern escalator.
The test rig is designed to conduct large scale fire
tests on inclined chamber escalator water suppression systems in a physical
environment representative of those found in the general working environment of
a sub-surface London Underground Limited escalator.
The fire load consists of four 3m long timber cribs made from kiln
dried soft wood timber with a 9-12% moisture content. Running along the upper
open space in the timber crib is a 20mm wide filled with general purpose grease
along its length. The cribs run along the same lines as the flammable parts,
the wheels and chains, of an escalator mechanism. The test rig is designed to
give the levels of shielding to water spray found in practice and the crib
structure of the timber simulates the uneven surfaces of wheels and chain
links.
Wind
velocity through the rig has been matched to the maximum found in the machinery
spaces under the escalators. Air is forced into the test rig using a fan fixed
at 30 degrees to the vertical in the purpose built housing. The fan speed is
adjusted so that a hot wire anemometer reads a minimum 1m/s along the length of
the test bed at all levels and at the exhaust opening. The increasing oxygen
flow into the fire encourages the spread of flame up the cribs.
A total
of 500ml of petrol is used to soak four 12mm thick, 140mm square pieces of low
density fibreboard on both sides. These pieces of fibreboard are attached to
the lower end of each crib using 20mm wide metal 'L' brackets so the fibreboard
does not fall away on burning.
One litre
of petrol is used as the ignition source in two horizontal trays with 20mm
sides and baffles at each end to stop the flame peaking at the centre. The
petrol is lit using a 1.5m long rod with a blowtorch taped to the end, by a
competent person in fire fighting personal protective equipment.
The main outcome of the testing is visual inspection during and after testing. During testing the length of crib burning, not length of flame, indicates the size of fire in the rig. This relates to the pass-fail criteria, which is to suppress or control the fire to prevent it increasing.
The suppression system will run for 30 minute duration
or until the fire is judged to have been completely extinguished. Scotch Mist
was able to extinguish the fire and therefore obtained a better-than-pass
result in only a matter of minutes.