Fan handles explosive gases

Ethylene oxide (EO) gas kills all known bacteria and their endospores, mould and fungi and is highly effective in sterilising materials that would be damaged by pasteurisation or Gamma radiation.

Sterilisation of everything used in a hospital is absolutely critical, and not everything medical can withstand the high temperatures necessary to bring about absolute sterility.

Items such a soft rubber goods, surgical implants, intravenous kits and the like would all be damaged by high temperatures.

One option is gaseous sterilisation.

Ethylene oxide (EO) gas kills all known bacteria and their endospores, mould and fungi and is highly effective in sterilising materials that would be damaged by pasteurisation or Gamma radiation.

Unfortunately, EO is carcinogenic, toxic, highly flammable, potentially explosive and gasifies at 10C.

Its use therefore requires great care and the design of EO sterilisation plant is highly specialised.

All electrical and mechanical equipment must be fully compliant with hazardous area standards.

Getinge UK of Sutton-in-Ashfield are a centre of excellence in the design and construction of EO sterilisation systems and install bespoke sterilisation plants worldwide for manufacturers of medical devices, sterilisation contractors and other healthcare product manufacturers.

In a typical system, pallets of the products to be sterilised are placed in a conditioning area where the temperature is raised to around 55C and the humidity to around 70% relative humidity.

This 'activates' any microbes and renders them more susceptible to the EO gas.

The pallets are then loaded into the hermetically sealed sterilisation chamber and the integrity of the chamber is confirmed with a vacuum test.

The chamber is then flooded with EO gas at below atmospheric pressure and the temperature maintained at the conditioning level by circulating heated water round a water jacket surrounding the chamber.

During the typically 12 hour period the goods are exposed, it is critical that the EO gas is maintained as a homogenous environment throughout the chamber.

To achieve this a specially designed explosion-proof Halifax Fan blower is used to continuously circulate the gas through manifolds on the sides and top of the chamber, changing the entire volume of the chamber typically eight to 10 times per hour, eliminating gas stratification and ensuring that the gas penetrates every nook and cranny.

Once sterilisation is complete, the chamber must be progressively flushed with nitrogen while the EO gas mixture is bled off through a catalytic convertor that converts the EO to CO2 and water.

The Halifax blower continues to circulate the gas mixture in the chamber as the gases are of different densities and would stratify if not actively circulated.

Once the concentration of EO is reduced to the point where it is safe to introduce air to the chamber, the pallets are moved to the post-condition area where the temperature is elevated to aid the degasification process.

The potentially explosive nature of ethylene oxide means that the circulating blower has to be designed to meet the exact needs of every installation and to full explosion-proof standards.

Halifax' stainless steel 316 shaft is fitted with a dual-cartridge mechanical shaft seal purged and cooled with water.

The fan is rated to work down to subatmospheric pressures but the high-integrity, gas-tight, stainless-steel casing is designed to operate at 10bar and tested to +11bar.

ATEX certified stainless-steel inlet and outlet flame arrestors protect against potential flame propagation beyond the fan in the event of internal combustion.

ATEX certified accelerometers and vibration monitors are included for early detection of any imbalance in the fan impeller that might lead to contact with the casing, potentially causing a spark.

According to Shaun Riley, EO Product Specialist at Getinge, "Although some of our competitors build their own blowers, we attach so much importance to this item that we wanted it designed, built and certified by specialists and supplied as a reliable fit-and-forget fully certified component".

"The hazardous nature of Ethylene Oxide meant that we wanted to deal with a manufacturer with a proven expertise in ATEX and hazardous gas applications".

"Halifax worked closely with us to develop a range of bespoke blower sizes that we can use for quotation purposes and then, once we have a contract settled, the blower design is fine tuned to the exact specification of that application".

"Although the blower comes to us fully certified to ATEX 94/9/EC for Category 2G, Zone 1, it is actually fully rated for duty at Category 1G, Zone 0, meeting the most demanding specifications of all our applications".

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