Calculations Leaks For leaks, you can assume that a 50 mm diameter hole is a representative event. When determining release rates for liquefied gas releases the formula for a liquid release ignoring the effect of liquid head may be used. A discharge coefficient of 0.6 can be applied in release calculations. It is assumed that the inventory of HCl is contained wholly within the recycle line and any backflow of HCl from the rest of the process can be ignored. Dispersion For flashing liquid releases, you should assume that all of the release enters the vapor cloud. For all calculations an ambient temperature of 15C, a windspeed of 5 m/s and a neutral (C) atmospheric stability should be assumed. When calculating atmospheric dispersion, the dispersion coefficients (for C Stability) may be calculated by the following formulae: y = 104x 0.984 , z = 61x 0.911 where y and z are in m and x is downwind distance in km. All releases should be treated as continuous (you may wish to comment on this) Jet Fires For jet fires, only direct flame engulfment need be considered. You should assume that people indoors are unprotected from direct flame engulfment. In the event of direct flame engulfment it can be assumed that there are 100% fatalities indoors (unless the building is specifically designed to withstand this event) and 100% fatalities outdoors. Flash Fires and VCEs Page 2 of 3 For flash fires you can assume that there are 100% fatalities within the flammable cloud (determined by the concentration contour to the Lower Flammable Limit) for outdoor populations and 50% for indoor populations for naturally ventilated buildings. For VCEs, assume that the whole of a congested volume is filled with a stoichiometric mixture of ethylene. Toxicity For toxic releases, assume exposure time is limited to release duration. For toxic clouds assume that indoor fatality rate equals half of the corresponding outdoor fatality rate. All releases should be assumed to be in the centre of the relevant area. For toxicity calculations the following Probit constants should be used: Table 2. Probit constants where time is in minutes and concentration is in mg/m3 Blast Overpressure The following vulnerabilities to blast overpressure apply to indoor populations: Table 3. Building occupant vulnerability to blast overpressure Hazard Zones Assume that if a hazard zone reaches the edge of a population the whole of that population will experience the same fatality rates (separately for indoor and outdoor populations). Where the consequences are dependent on the direction of an event, four possible directions event to North, East, South and West should be considered. Any population within range and within the relevant sector (within 45 either side of the direction) can be exposed to the event. Separation distances are provided below: Table 4. Separation distances (centre of source to edge of target) Page 3 of 3 Escalation Pipework and vessel rupture is possible if flame engulfment exceeds 15 minutes. Pipework rupture is possible if blast overpressure exceeds 200mbar. The possibility of vessel rupture due to blast overpressure can be ignored. For each area, escalation should be assumed if these thresholds are exceeded at any point in the respective area. Vessel failures in the process area can be discounted (vessel inventories are small in this area). For rupture of a vessel containing a toxic material, it can be assumed that the contents are released over a period of 60 seconds leading to an exposure time of 5 minutes.