Technology and process
Halon fire extinguishers packed
on pallets for transport
Halon fire extinguishers are surrendered or deposited by individuals or small businesses at fire stations in all states and territories.
Halon is a non-toxic non-flammable gas. However, as a gas under pressure there is a danger if cylinders are ruptured during transport.
Special packing and transport is arranged by the National Halon Bank to move the halon extinguishers to the disposal plant in suburban Melbourne.
Halon received at the National Halon Bank is removed from its container and placed into bulk storage pending safe disposal. This process is called decanting. In order to determine how much halon has been recovered, each cylinder (for large cylinders) or pallet (for small cylinders or extinguishers) is weighed. The decanting process involves puncturing the pressure cylinder and draining the content and then drawing a vacuum on the cylinder to volatilise any residue remaining in the container, then flushing the cylinder with nitrogen.
Decanting and recovery rig showing cylinder piercing technique
The halon recovered from cylinders may contain a number of impurities. Common contaminants such as oil, dust water, carbon dioxide and nitrogen are often found in bulk cylinders which have been used to recover halon from other systems. These contaminants are removed, using specialised equipment, in a process know as reclamation.
The halon recovered is tested to determine the purity level and is then placed in permanent bulk storage containers to await disposal or reserved for sale.
Reclamation returns the halon to 'as new' specification.
The resulting weight of halon, water, oil and empty cylinders is compared to the original weight of the filled cylinders to ensure that all material is accounted for.
PLASCON rig installed at the National Halon Bank
Halon is disposed of by heat degradation using specialised technology, developed in Australia by the CSIRO and SRL Plasma Pty Ltd. The report CMPS&F - Environment Australia - Appropriate Technologies for the Treatment of Scheduled Wastes - Review Report Number 4 - November 1997: 13. Plasma Arc Systems contains a comparative assessment of waste disposal technologies.
Further information, including process overview and a case study on the National Halon Bank can be found on the SRL PLasma website.
The PLASCON process involves injecting the halon directly into a plasma arc, quenching the resulting gas with caustic soda and disposing of the brine.
The process does not involve burning, or oxidation, rather the molecules are destroyed and the halon returns to its constituent atoms. There is therefore no formation of dioxins or furans.
This brine solution is disposed of under licence for treatment by City West Water.
The PLASCON process achieves a destruction efficiency of 99.9999% for halon and other chlorofluorocarbons, hydrochlorofluorocarbons and hydrofluorocarbons.
The challenge for the National Halon Bank is to preserve a scarce and valuable resource for a up to 30 years, without loss or degradation.
Fixed floor level leak detection
The Department of Sustainability, Environment, Water, Population and Communities has determined the quantity of halon to be retained through consultation with industry users. Allowing a margin for error and any unforeseen demand 200 tonnes of Halon 1301 and 70 tonnes of Halon 1211 have been set aside. The Halon 1301 is packed in 500kg cylinders in a controlled environment. The Halon 1211 is stored in 25 tonne bulk tanks.
Liquid level measurement
The stockpile is actively managed to reduce the possibility of leaks, which would result in loss of a vital and irreplaceable resource and damage to the Ozone Layer.
Regular monitoring and stock weighing processes are employed to ensure the integrity of the stockpile. These processes include automatic 24 hour per day ground level leak detection.
Trials have also been undertaken to determine the accuracy of measuring the liquid level within a cylinder as an alternative to weighing the cylinder. Once the accuracy and consistency of the process has been established liquid level measuring will replace routine weighing.