AWN Consulting was commissioned to assess the Major Accident Hazards (MAHs) associated with proposed changes to a large Integrated Circuit Manufacturing Facility in Eastern Ireland.

Proposed changes included the construction of bulk hydrogen storage tanks, a bulk oxygen storage tank, a nitrogen plant and a Bulk Specialty Gas System (BSGS). The worst case MAH scenarios were identified as a hydrogen or oxygen Boiling Liquid Expanding Vapour Explosion (BLEVE), failure of bulk nitrogen containment causing an oxygen diminished environment and the release of dangerous substances including ammonia and hydrogen chloride from the BSGS.

The impacts of these MAH scenarios were modelled using DNV PHAST software. The overpressure and thermal radiation levels associated with oxygen and hydrogen BLEVEs were calculated and contours corresponding to the Health and Safety Authority (HSA) inner, middle and outer land use planning zones were mapped. Where MAH scenarios gave rise to overpressure and thermal impacts off-site, the risks were quantified using Fault Tree Analysis (FTA). It was concluded that any off-site risks are well below the accepted risk of fatality of 1 x 10-6/year as defined by the HSA.

In the event of failure of bulk nitrogen containment, maximum distances and durations at which the concentration of nitrogen will be equivalent to Emergency Response Planning Guideline (ERPG) values (for nitrogen) were determined, which are based on 1 hour exposure durations. The maximum exposure duration to nitrogen at concentrations equivalent to ERPG levels are well below the 1 hour duration. Therefore no off site impacts are predicted to arise as a result of this scenario. In relation to the BSGS, the impacts of an accidental release of ammonia due to catastrophic rupture of the storage vessel were assessed. It is concluded that no off site impacts will arise as a result of this scenario. An assessment was conducted of the impacts of a hydrogen chloride release due to catastrophic rupture of the storage vessel. It was concluded that no off-site impacts will arise as a result of this scenario.