Gas cabinets are ventilated enclosures for safely storing and delivering toxic or hazardous gas cylinders in semiconductor fabs. Purpose: Contain and detect leaks, provide controlled delivery, protect personnel from exposure to dangerous gases. Gases stored: Toxic gases like phosphine (PH3), arsine (AsH3), boron trifluoride (BF3), hydrogen chloride (HCl). Also pyrophoric gases like silane. Features: Continuous exhaust ventilation, gas leak detectors, automatic cylinder valve closure on alarm, sprinkler protection, seismic restraints. Monitoring: Toxic gas monitors inside cabinet and in surrounding area. Tied to fab safety systems for evacuation alarms. Access control: Locked access, change procedures for cylinder replacement, trained personnel only. Delivery system: Regulators, purge systems, molecular filter/purifiers, delivery piping all within or connected to cabinet. Cylinder restraints: Chains or brackets to secure cylinders against seismic events. Cabinet exhaust: Dedicated exhaust to toxic gas scrubber. Negative pressure inside cabinet. Compliance: Meets fire codes, SEMI safety guidelines, insurance requirements.