Dealing with CLEA 50% MDI Rule.
For such an innocuous little rule, it really does cause a programming and algorithmic headache.
What many people won't appreciate is that if there is an MDI contribution and you are considering both oral and inhalation pathways, then the CLEA SR documentation doesn't actually provide you with all the necessary equations to calculate GAC/SAC. Which, when you think about it, is somewhat of an oversight!
The EA CLEA model uses the Excel Goal Seek function to solve the problem - that's why it needs re-running every time you change anything (time for surfing at least while it chunks away).
Goal Seek, to put it crudely, is a guessing function: you know the answer and Excel tries to tell you how you got there. Basically, Excel keeps refining its guess until it gets a/the solution.
What Meng Fangs excellent equations do is by-pass all that nonsense and allow you to calculate directly. Genius.
We implemented his pre-published equations into our CLEA model and they work perfectly. Change parameters - outputs updated immediately, with results spot on to EA CLEA.
Question is, is there a simpler way for the EA to implement some form of a 50% MDI rule to avoid these additional calculations (added complexity, for no real gain in accuracy?).
One way could be to separately ensure that oral MDI contribution never exceed 50% for oral pathways and inhalation MDI contribution never exceed 50% of inhalation pathways, rather than trying to limit overall MDI to 50% across both Oral & Inhalation pathways (ie adopt simple TDSI calculation). Would need to look at that in more detail to see actual consequences on outputs (been a while since I've thought about it).
Or like the rest (most?) of the world, bin the whole idea of taking into account MDI.
Kind regards
Chris Dainton
Peak Environmental Solutions Limited
Unit 10, Aston Ind Estate, Parsons Lane, Hope, Hope Valley, Derbyshire, S33 6RB
Tel: 01433 620030
www.peakenvironmentalsolutions.com
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