Hazardous materials Modular systems
In a modular or DLP or ILP system, the key element is the burst tube – which acts as a detection device. The tubes are specifi cally manufactured thermoplastic sealed units which are designed to rupture at a specifi ed temperature, usually 70ºC (for comparison, the most commonly used sprinkler heads operate at 68ºC). The benefi ts of direct and indirect modular systems are: •
fl exibility afforded to the specifi er in respect of the choice of the most appropriate agent for the risk
• ease of installation • •
low probabilities of spurious actuation lower recharge quantities and cost
• cost effective transport •
low costs both of installation and maintenance
• cylinders can be located inside the protected space – even inside a cabinet or engine bay
Direct and indirect modular systems are essentially agent delivery systems and a wide choice of firefighting agents1
typically including: • dry powder (ABC) • chemical gases (eg Novec 1230) • water and watermist •
foam/water solutions
inert gases (eg nitrogen) Of the commonly used agents, only carbon dioxide would not be appropriate in the modular systems presently available – this is due to the pressure under which the CO2 gas is stored.
• wet chemical (Class F) •
Structure and layout
DLP or ILP systems using burst tubes rely on the stored pressure that is contained in the detection tubing and the agent storage cylinder. The most frequently used pressurisation gas for powder and liquids is nitrogen. The detection tubing is extremely fl exible and can be run extensively through the protected area. Once the tube bursts, it releases the pressure of the detection tubing, which then creates a differential pressure in the valves located in the top of the cylinder(s).
As the tubing is normally charged
to 10-20 bar/140-280psi, the moment the tube ‘sees’ a flame it will burst due to the differential pressure between the atmosphere and the pressure in the tube.
is available,
FOCUS
Burst tube connected to differential valve System types
Burst tube systems using low pressure (maximum 20 bar) can be divided into two types: direct and indirect. In the direct system, the burst tube acts as a detection device and also a discharge mechanism. Some manufacturers now offer direct systems which are totally self contained, with no requirement for an external power supply – a major advantage in systems such as those fitted in mobile plant or vehicles.
A direct system
Indirect systems use the burst tube solely as a detection device; when it loses pressure due to the effect of external heat, this actuates the sophisticated differential pressure valve. This then discharges the agent down a separate system of stainless steel pipework or a discharge hose, which will be fi tted with nozzles to direct the agent to the desired locations.
An indirect system
www.frmjournal.com APRIL 2018 33
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