Fume Cupboards or Fume Hoods are a specific class of Local Exhaust Ventilation (LEV) equipment. They are ventilated enclosures designed to limit exposure to hazardous or toxic fumes, vapours or fine airborne particulate. Fume cupboards may also provide spillage protection and in some causes explosion protection.
Two main types exist, ducted and re-circulating (ductless). The principle is the same for both types, air is drawn in through an aperture at the front of the unit and either vented to atmosphere via a ducted extract system or filtered and discharged back into the room.
Tecomak provide a comprehensive fume cupboard service, including fume hood servicing, for all types and makes of ducted and recirculating cabinets.
Ducted Fume Cupboards
Most industrial fume cupboards are ducted and disperse the contaminated air externally outside the building, usually above roof level by means of discharge stack. Ducted fume cupboards generally offer higher levels of operator protection than re-circulating fume cupboards and can be used to control a wide variety of substances.
Ducted Fume Cupboards should be certified to comply with ‘BS EN 14175-2:2003 Fume Cupboards, Safety and performance requirements’.
There are two main categories of ducted fume cupboards :
Constant Air Volume (CAV)
These are designed to maintain a constant air extraction volume no matter where the sash is positioned. Face velocities will vary depending on where the sash is set and will increase as the sash is closed. Air bypass openings situated near the sash ensure that changes in face velocity are kept within a specified range. Depending on design, fume cupboard sashes may move vertically, horizontally or in combination.
Variable Air Volume (VAV)
These units use sash positioning controls to vary the fume cupboard extract fan speeds and subsequently alter the air extract volume. The extract volume varies depending on where the sash is positioned and allows face velocities to remain constant, at a predetermined level. The systems may be linked to building monitoring systems to enable extract and room make up air to be balanced.
Re-circulating / Ductless Fume Cupboards
These are self-contained units in which the exhaust air is passed through a filtration system and discharged back into the room. Filters must be matched to the class of chemicals to be used and have a limited absorbent capacity. Care must be taken to ensure this limit is not exceeded as it can result in the release of hazardous substances into the work environment.
These units are not suitable for work involving radioactive, highly toxic, carcinogenic or sensitising substances. It should be noted that HSE do not recommend using these fume cupboards for exposure control of vapours or carbon nanotubes (HSE Control Guidance note 201 and HSE Risk Management of Carbon Nanotubes 2009).
Re-circulating Fume Cupboards should be certified to comply with BS 7989:2001 ‘Specification for recirculatory filtration fume cupboards’. Tecomak provides a regular fume cupboard service, including testing and maintenance for all models.