Ozone safety assurance during operation of 10 MeV RF electron linac by developing an air flow sensor and using ozone level monitor and interlock

A lot of ozone gas is produced due to breaking of air particles present in between the beam exit window of Linac and products to be irradiated. Though the ozone gas is non-poisonous, non-hazardous and non-toxic, being much heavier than oxygen, it creates a depletion of oxygen near the scan horn area of LINAC. The allowable level of ozone is 100 ppb for the human occupancy. There is a 2.6 meter thick mild steel mobile shield for entering the operating personnel after irradiation near the scan horn area of LINAC. Two 20 HP ozone removal pumps are in operation to remove the ozone produced due to Linac operation, via 12 earth pits made in the irradiation area of LINAC. The human safety is ensured by continuously monitoring the ozone level (analog signal), the ozone removal speed by measuring air flow signals (analog signal) at different pits, the ON/OFF status (DI) of two pumps and interlocking the mobile shield opening with the 100 ppb level of ozone level. A potential free contact is generated against the 100 ppb level in the ozone monitor. An Air flow sensor with two analog inputs and two alarm outputs have been developed to ensure the ozone removal at various pits. A light transmitter-receiver is mounted at the two ends of the rotating fan, which rotates due to air flow. The count of light pulses is calibrated with the air flow speed. This paper discusses the details of the measures taken to ensure human safety against ozone produced during operation of LINAC. (author)