I would like to think that this distance is the result of someone at some time running a model of dispersal of a chlorine leak under given weather conditions. But who knows - it could be a guess. Have you got the HSE guidance for chlorine cylinders, HSG40?

I agree that HSG 40 is the current industry guidance. However having personally witnessed a leak from a 33kg chlorine cylinder, the 20m distance quoted in HSG 40 is too little. On that occasion a house was located approximately 30m away: the escaping chlorine stripped all of the paint and varnish off all of the fixtures in the house, and attacked the soft furnishings to the point where they had to be dumped (a 1m high "tide" mark showing the gas cloud damage was visible in the house after the leak). Thankfully the residents escaped as one of them worked with chlorine (unconnected with the leak). and immediately recognised it when it started entering their house: all safely evacuated.

I'd be pretty interested in wind direction too! Do you have a wind sock on or near the compound? Phil

The recognised way of resolving this would be to undertake a consequence modelling exercise. This is usually done using the DNV PHAST software.

I would expect the chlorine in the bottle to be a liquid.

To keep below the WEL the safety distance could be up to 1350m (0.5ppm) 900m for 1ppm 550m for 2.5ppm 350m for 5ppm Possibly lethal for 33% of people to 30m AT about 70m, 10% lethal I would set your safety distance to maybe 250m

Chlorine gas cylinder storage is an intrinsic part of my current sites operation of etching metal with ferric chloride. At your level of usage all the pertinent points have been covered already and reference documents given. To give you my scenario which mostly backs up what others have said, we have sensors in all the areas that it is used. We have a high and low level leak alarm and a trained team of incident responders (face masks, face fit tested, gasman detectors etc etc). Our cylinders are stored in a brick shed outside and should we have a leak our first assembly point is inside the main building in a large office at the front of site. If a leak is detected in the usage areas again we close all windows, doors and proceed to the internal assembly point - its worth pointing out that should a low level alarm occur then the system is automatically shut down. Its hard to fully go into detail of our system without writing an essay but the whole system and emergency procedure has been developed with Siemens and Inios Chlor. We also have trained spill responders to deal with liquid chlorine spills using sand etc. The sensors go off well before the human nose can detect it and my god its a strong bleach smell! Treat the stuff with the respect it deserves and you won't go far wrong.

In the event of catastrophic failure and liquid release the distance to 147 ppm is: 140 m under D5 weather conditions 117 under F2 conditions.

114 metres is hardly in the next village. Distances are calculated rather than plucked from the air.

It may be 100% safety distance but that's not possible - low risk not no risk. Not even Usain Bolt would relish a 100+M dash and in most circumstances this really is a hell of a long way, certainly off your own premises, over someone's elses and maybe into another (exception being big facilities) There was a post the other day with a similar theme and the distance was given as 400+M. Again , wont argue with 100% safety distance but it is totally 100% impossible to get there in time and to have control over such a place so far remote. There needs to be a degree of common sense of what is actually achievable.

3,064 is the duration of release, then there is time of cloud drift and an assumption of exposure upto the hour.

Post 16 relates to instantaneous catastrophic failure releasing total inventory of liquid chlorine. Post 15 relates to release of time.