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Posted By Mike DF
Whilst reading through the HSE book 'controlling airborne contaminants at work' I noticed that the use of chinese hats to cover LEV stacks is never to be used...then I took a look at what our professional installers have done - chinese hats on every stack.
I appreciate the reasons for (stop rain) and reasons against (directs exhaust downwards), now I need to get the contractors in to do the job properly. Does anyone have any experience of this? I would think that the contractor should pay for the work but it will cost a few £ to make the stacks waterproof so I guess I am up for a scrap.
Your comments will be appreciated
Thanks
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Posted By Ian Blenkharn
It depends on what pollutants you are trying to exhaust.
Stacks should be of suitable height and in a location that ensures free dilution and dispersal, and must not be affected by surrounding structures, wind speed or direction. Mathematical monitoring is available for critical systems. Location is even more important than the use of any baffle but as always its a complex situation and all of these factors have a bearing on safety.
The problem with chinese hats is that they deflect the outflow downward, and that may be in the direction of an air intake or window etc, or allow particulates (there shouldn't be any, but...!) to fall in locally high concentration in a relatively small area.
You can also get condensates forming on the inner surface and dripping down from the lip but that might, if you're lucky, dissuade birds from nesting
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Posted By Paul Leadbetter Mike At the very least, you should turn the 'chinese hats' upside down but you will need to add a drain to the centre of the hat to get rid of any rain that collects. More effective terminations can be found in the ACGIH Industrial Ventilation Manual; in my 23rd edition, they are on page 5-66. If contractors are still fitting inappropriate terminations, I would have to question their competence. Next time you need a system installed, talk to a competent occupational hygienist; find a local one here: http://www.bohs.org/reso...ants_directory100408.pdfPaul
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Posted By Andy Petrie
Paul,
is it usual for occupational hygienists to be designing exhaust stacks? (I'm not being sarcastic by the way, just really don't know)
I would have thought speak to a competent mechanical/process engineer would have been better advice.
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Posted By Paul Leadbetter
Andy
Mechanical engineers can make sure that the system won't fall down but, unless they are trained in lev design, they won't know about terminations, fan sizes, etc, as you appear to have found out.
As a hygienist, I know how to design a system but not how to make sure it doesn't fall down (!) so you really need input from both disciplines.
However, I would expect a competent ventilation engineer to have, or to at least have access to, both sets of skills.
Paul
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Posted By Paul Leadbetter
Sorry, Andy
I have confused you with Mike DF.
Paul
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