Welcome Guest! The IOSH forums are a free resource to both members and non-members. Login or register to use them

Postings made by forum users are personal opinions. IOSH is not responsible for the content or accuracy of any of the information contained in forum postings. Please carefully consider any advice you receive.

Notification

Icon
Error

Options
Go to last post Go to first unread
Evans38006  
#1 Posted : 09 April 2018 13:07:49(UTC)
Rank: New forum user
Evans38006

Hi, 

Looking for the online calcualtion for gas dispersion - specifically I am trying to look at the dispersion for ammonia in case of a catastrophic leak.  I know there was an online calucator but I just cant find it!

Thanks for any help,

boblewis  
#2 Posted : 09 April 2018 19:35:32(UTC)
Rank: Super forum user
boblewis

All dispersion models are complex and are really design engineers tools not the routine H&S person.  Water Fog curtains are always the best protection to prevent ammonia spread and you should be looking towards this and employing an expert for the dispersion modelling.

A Kurdziel  
#3 Posted : 10 April 2018 09:52:56(UTC)
Rank: Super forum user
A Kurdziel

I looked at this yesterday but the only thing I could find was various scientific papers explaining why this or that method was wrong! The subject is very technical as there are so many factors which can vary such as wind direction, if it is raining or not, how warm it is, whether the gas leaks slowly or as a fast jet. You need some sort of consultant to do this. They will have to look at your site and decide what will apply to you.

Steve e ashton  
#4 Posted : 10 April 2018 10:49:59(UTC)
Rank: Super forum user
Steve e ashton

Is this what you were looking for? (If the link doesn't work, Google offsite consequence analysis)

https://www.google.co.uk...aw1xil5XbstPb1GZOULCGYXP

I have delivered a number of major accident plans which did not include quantitative analysis. Often a qualitative assessment will suffice, and may actually be more reliable for many scenarios because the number of variables in most quantitative tools can introduce errors of several orders of magnitude if not properly accounted for. As others have said, rain, fog, installed protections, wind speed, buildings, water courses, ground permeability etc must all be factored in to any analysis. Sometimes it can be best to estimate from previous leaks and catastrophic releases. Call it guesswork, but my hastily drawn plumes for a fertiliser factory 100kl anhydrous sphere in Ukraine matched within 100ft the calculated plumes achieved from several weeks of number crunching.
And don't forget, if its anhydrous ammonia, there are potential explosion risks which may be more catastrophic than downwind plume toxicity... Google Jonshaven blast in Lithuania for one example from memory.
Ian Bell2  
#5 Posted : 11 April 2018 05:25:17(UTC)
Rank: Super forum user
Ian Bell2

As indicated, anything like reasonably accurate dispersion models are not straightforward with the many variables that could/Should be factored I to the calculation.

PHAST software is normally used in dispersion modelling, but this is very expensive software for a 1-off use.

It's normal to assess dispersion under 2 weather conditions, for outside dispersion, D5 and F2 using the Pasquall-Gifford method.

There are text books available to help. Free resources include publications by the Dutch government published in the 1990s about how to calculate dispersion known as the Red, Green and Yellow books which give guidance on QRA, forums for modelling gas and liquid leaks etc.

The maths rapidly gets interesting.
thanks 1 user thanked Ian Bell2 for this useful post.
Steve e ashton on 11/04/2018(UTC)
Ian Bell2  
#6 Posted : 11 April 2018 05:30:02(UTC)
Rank: Super forum user
Ian Bell2

stevedm  
#7 Posted : 14 April 2018 08:06:43(UTC)
Rank: Super forum user
stevedm

There are a couple of free dispersion calculators not maybe as accurate as PHAST or Safeti or Risk Curves...

ALOHA is a free software for emergency planning from the US EPA

https://www.epa.gov/cameo/aloha-software

WISER is also another us system for emergency responders

https://webwiser.nlm.nih.gov/getHomeData.do;jsessionid=0C8724398A6D85B029CA526C15F3BBD1

Both can give uk mapping and google earth overlays (if you know how) and have the correct coordinates.

If you need any more give me a shout...

stevedm  
#8 Posted : 14 April 2018 08:18:20(UTC)
Rank: Super forum user
stevedm

As a wee add in....all of these you will need the environmental conditions including wind direction etc for all the scenarios you are looking at...

There are some downloads for google earth from this supplier which help and some other free tools..

https://www.enviroware.com/create-your-wind-roses-on-line/

Users browsing this topic
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.