a 24-hour technical exhaust air system, then the hazardous area is limited to the inside of the cabinet. To prevent damage to the cabinet by corrosion, no acids or alkalis may be accommodated in this type of cabinet: TRbF Appendix L: Storage equipment in working areas (safety cabinets)/ points 4.1 and 4.2 as well as BGR 104 2.2.8). If the connection to an exhaust air system is not possible on site, solvent and safety cabinets can be technically ventilated with a recirculating air filter unit. These units filter the exhaust air from the cabinet through an activated carbon filter, capturing harmful vapors and returning the cleaned air to the working environment. Function In the event of a fire and the attainment of an ambient temperature of 50 °C (+0/−10 °C), the drawers, if fitted, must first retract and the doors must automatically close. These actions are normally activated by bimetallic or fusible links. At approx. 70 °C, the fire protection valves in the fresh air inlets and exhaust air connection points auto-close. From an ambient temperature of approx. 160 °C, the intumescent seals foam up and expand to seal the joints at the doors. The cabinet is thus hermetically sealed. Safety cabinets with automatic door closing provide additional security. After a defined time interval, the cabinets close automatically, thus minimizing the exposure of the stored chemicals and reducing the risk of escaping hazardous vapors. In modern safety cabinets, a visual and acoustic warning signal is given when the door is closed. Safety cabinets for compressed gas cylinders do not have an automatic door closing function, as the doors of these cabinets must always be closed during operation. Performance In line with the fire rating, the safety cabinet prevents the stored goods from heating up over the specified length of time. For example, a Type 30 BS EN cabinet will guarantee 30 minutes of safety before the internal temperature becomes critical. A Type 90 BS EN cabinet offers maximum safety with 90 minutes protection. For flammable liquids and solids, this temperature rise is 180 °C (K) and for pressurized gas cylinders, the permissible temperature rise is 50 °C (K). Testing is conducted as a freestanding single cabinet in a suitable fire chamber. The entire cabinet must be exposed to the same heating conditions. The temperature rise is measured inside the cabinet according to the Unit Temperature Curve (ETK). Inspection and service