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Deflagration / Fast-Fire Protection Systems for Aerosol Gas Charging Room – IEP Technologies
Application
A typical aerosol packaging line is an automated system, incorporating conveyor systems and automated filling and charging systems. Aerosol cans are charged with various propellants. Most commonly these propellants are flammable hydrocarbons such as DME (dimethyl ether), Dymel® 152a, propane, butane, isobutane, or a blend of these hydrocarbon gases. These propellants are introduced into aerosol cans by high speed filling machines, some of which are capable of fill rates up to 450 cans per minute. There are usually a number of personnel involved in the filling line operation to verify proper operation of the equipment, to remove damaged containers, and to provide maintenance or to shut down the line in case of a problem. Thus, the personnel may be present in the room while the risk of a deflagration exists within the gas charging room.
Hazard Analysis
If flammable propellants are used during aerosol charging operations then the potential for a deflagration event exists. During normal operation a small level of propellant is released. However this is normally diluted by the large air changes mandated by aerosol gas charging room design. Fill equipment jams, failure of charging lines, material defects, or improperly sealed aerosol cans can cause hazards. While the amount of gas released may not be sufficient to cause a deflagration if evenly distributed, local concentrations of flammable gas can produce a fireball posing a significant threat to personnel. These flammable gas releases only require low energies for ignition and are frequently ignited by static discharges created by the flow of the released flammable gas or mechanical friction caused by malfunctioning equipment. The immediate nature of this ignition source means that the deflagration often occurs well before gas detectors can detect elevated gas levels.
Protection System Description
The aerosol gas charging room protection system is designed to satisfy the deflagration suppression system requirements listed in the National Fire Protection Association (NFPA) Standard No. 30B for aerosol filling facilities. The system design is based on suppressing a localised deflagration from the ignition of the hydrocarbon propellant gases. The system utilises high-rate discharge (HRD) suppressors filled with distilled water as the suppressant. The HRD suppressors are mounted indoors at an ambient temperature above the freezing point of distilled water. The system uses ultraviolet/infrared (UV/IR) sensors mounted in the room that detect deflagrations in areas which standard flammable hydrocarbons are utilised as the propellant. Upon detecting a deflagration, the detectors transmit a signal to the control panel.
This triggers HRD suppressors to discharge suppressant in an effort to suppress the fireball. Simultaneously, the control panel interlocks with the protected components and associated process equipment, in order to shut down conveyor drives, gas solenoids, and hydrocarbon pumps inside the room to prevent spread of burning material and to minimise possibility of re-ignition occurring. The exhaust fans are signalled to operate at maximum speed to extract any remaining vapours in the room.
