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SPECIALIST LEV

Gas Safety Cabinets

A gas cylinder storage cabinet is designed to provide safe containment of gas cylinders when they are installed within buildings. They provide physical protection, fire separation and ventilation to safely disperse any leaks that may occur.

Gas cylinders storage cabinets must have the following features:

  • Be of fire resisting construction offering at least 30 minutes protection against fire
  • Be provided with forced extract ventilation discharged to a safe location. For flammable gases the ducting will need to be fire resisting up to the point of any damper
  • Have inlet and extract points fitted with automatic dampers to cut off air supply in the event the cabinet is exposed to a fire
  • Be labelled to give an indication of the nature of the hazards of the gas

The following guidance should be followed:

  • Gas cabinets should be dedicated to a specific gas or class of gases.
  • All joints which are regularly broken and re-made should be positioned inside the cabinet as well as all associated valves, regulators and connectors
  • Where possible, the air inside cabinets containing toxic gases and/or flammable gases should be monitored, with alarms, to detect leaks
  • An alarm giving warning of extraction ventilation failure should be installed
  • The cylinder supply should be interlocked and therefore shutdown in the event of ventilation failure or gas detector alarm
  • The cabinet and all the equipment within the cabinet shall be electrically bonded to earth.

The cabinet shall be provided with sufficient extraction ventilation with the aim of containing small leaks of gas and minimise their escape to the workroom. However, it is accepted no ventilation system would be able to deal with a major escape of gas. The extract volume should maintain the potential concentration of leaking flammable gases in the extracted air to below 25% of the lower flammable limit, except in the event of a catastrophic leak.

Ventilated or ‘down flow’ benches

A ventilated / down flow bench is a bench which has a fume removal system driven by a fan. Contaminated air is extracted downwards through perforations in the bench work surface and through a central spigot. Ventilated / down flow benches can either be ducted to atmosphere or recirculating with carbon and HEPA filtration.

They are useful if working chemicals with low volatility and have been shown to be as successful as fume cupboards in dealing with contaminants. They have the advantage of allowing greatly improved access to the work area and can help reduce certain types of accidents such as those involving sharp implements. Ventilated / down flow benches are often used in dissection, autopsy or other histological work.

The limitations of these benches are that they may not contain projected particles as a result of an explosion and localised heating may adversely affect containment. Further, ventilated benches do not protect the user from bio hazardous substances – they are only useful for limiting potential exposure to fumes.

Unlike Laboratory Fume Cupboards, there is no set standard for use of ventilated / down flow benches. The requirements of the COSHH
Regulations should therefore be followed, including:

  • Checking the performance at least annually using either a measure of containment or average air inflow velocities
  • Conducting weekly or monthly visual checks to validate that the extract system is working
  • Changing filters at intervals recommended by the manufacturer/supplier

 

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