Chris
The concentrations you quote are high compared to the vapour permeability quoted for many membranes.
Have you asked the manufacturers to provide robust evidence - and are you happy to cover their advice to you with your PI? I have seen lots of expensive "hydrocarbon resistant" membrane specified where not needed (if your membrane is being attacked by vapours there are probably more serious concerns to addressed!
My view is that you should carry out an assessment of the effect of the membrane. There is no specific tool for this. You have to go back to first principles of vapour transport and use a calculator.
There is some evidence from USA monitoring studies that membranes alone are not good barriers.
Steve
Sent using BlackBerry® from Orange
-----Original Message-----
From: Chris Dainton <[log in to unmask]>
Sender: Contaminated Land Management Discussion List <[log in to unmask]>
Date: Wed, 4 Aug 2010 11:04:51
To: <[log in to unmask]>
Reply-To: Chris Dainton <[log in to unmask]>
Subject: Re: Contamination Depth & Indoor Vapour Levels
Hi Steve
Not sure by what you mean by 'very low allowable concentrations', as the allowable 'CLEA' indoor vapour concentration for speciated TPH fractions and TEX are actually (what I would consider) quite high ranging from 0.1 to 9.8 mg/m3, although additivity may need to be considered for TPH.
As a guide to put these TPH levels in context, the odour threshold for diesel is around 0.06 mg/m3. The odour threshold for toluene and xylenes are around 0.5 and 0.06 mg/m3 respectively.
Naphthalene, benzene & TMBs are much lower at 0.002, 0.003 and 0.002 mg/m3 (though the AQS for benzene of 0.005 mg/m3 might be more applicable). BaP should be considered non-volatile.
Chlorinated solvents are also low (<0.001 to 0.2 mg/m3).
Some of the membrane producers will now provide an assessment of site specific suitability of their membranes based on identified contaminant concentrations.
Chris Dainton
Peak Environmental Solutions
|