Class 1 definition: Safety cabinet with a front aperture through which the operator can carry out manipulations inside the cabinet and which is constructed so that the worker is protected and the escape of airborne particulate contamination generated within the cabinet is controlled by means of an inward airflow through the working front aperture and filtration of the exhaust air. CONSTRUCTION The new WL4E and WL4ES are made from stainless steel and is finished in white polyester powder coat paint for a durable, easy clean finish. The interior features a non-painted stainless steel floor with radiused corners to give a hard wearing surface which is easy to keep clean. The whole work area is evenly illuminated. The front edge has a raised arm rest to reduce operator fatigue. The steel night door is easily clamped into position, guaranteeing a gas tight seal without the need for taping, even during fumigation. A 6mm thick toughened glass window is hinged to allow easy access to the interior for cleaning, pre-filter changing and placing bulky objects inside. The anti-blowback valve is fitted adjacent to the HEPA filter, and combines an airflow indicator and the 'airflow out of limits' warning system. An intuitive touch operated control panel features a digital readout of air velocity and also an 'hours run' meter. AIR FILTRATION The main HEPA filter is used at only 75% of its rated capacity (with NaCI penetration not exceeding 0.003% when tested to BS3928) so that it is never over stressed.