VOC assessment and VOC membranes - Amazon Web Services · 2018-03-06 · VOC risk assessment –...
Transcript of VOC assessment and VOC membranes - Amazon Web Services · 2018-03-06 · VOC risk assessment –...
VOC assessment and VOC membranes
Steve Wilson www.epg-ltd.co.uk
The next 25 minutes • Current issues in VOC assessment – where it often goes
wrong ▫ VOC risk assessment process ▫ The CSM and understanding of building construction and
vapour pathways through the floor ▫ VOC membranes ▫ Internal or underfloor void monitoring with PIDs and laboratory
testing ▫ Basement VOC assessments – is it really a vapour issue?
VOC risk assessment – what should happen • Collect the right data • Critically assess the data • Develop a visual CSM • Critically assess CSM and define
what you are going to model • Develop the model or choose an
appropriate off the shelf one (there are several) that fits site and building
• Choose parameters • Do a bit of maths
Time and Effort Required
Note there is
nothing we use that is not in the public
domain
VOC risk assessment – what actually happens in a lot of cases • Collect the right data • Critically assess the data • Develop a visual CSM • Critically assess CSM and define what you are going to
model • Develop the model or choose an appropriate off the shelf one
(there are several) that fits site and building
• Ignore building construction, ground
model and use generic assumptions
• Use GACs or CLEA
Time and Effort
Ground model
• How deep is the contamination • What is the permeability and porosity of
the ground • Depth and nature of buried services –
will these provide a preferential pathway or not? They may not
• Ground improvement – will stone columns provide a preferential pathway? They may not
• Piled foundations – will they provide a preferential pathway – they are not likely to in most cases (paper by Wilson and Mortimer in Environmental Geotechnics (doi.org/10.1680/jenge.17.00009 Paper 17.00009)
Are generic assumptions reasonable?
• Reasonable quality reinforced concrete is often a sufficiently good barrier to vapour (and ground gas) providing pipes are cast in and internally sealed
• Where is the perimeter crack?
• Generic assumptions are over conservative
Are generic assumptions reasonable?
• Block and beam floor - leaky?
• Perimeter crack?
• Vented void - Good barrier? • Odour threshold exceeded in
void?
Remediation using VOC membranes
• Do not assume a membrane will break the pathway • Consultants need to take a stronger role in assessing
membrane suitability and design – signed of by Chartered professionals
• Membrane suppliers are not qualified to make assessments about the suitability of membranes to deal with VOCs – they are not risk assessors
• VOCs permeate through membranes at different rates dependent on: ▫ Concentration gradient ▫ Membrane material ▫ Thickness ▫ Solubility of the contaminant in the polymer ▫ Shape and size of the contaminant molecule
Supplier assessment
• Supplier stated “We have reviewed the attached report and noted there are hydrocarbons on site which would require a Hydrocarbon resistant membrane such as the ACME SUPER DUPER VOC BARRIER”
• Supplier highlighted report • Only contaminants are PAHs that are
not sufficiently volatile to pose a vapour intrusion risk
• Reference to “hazardous” is in relation to waste classification
• In fact there was no need for any VOC or gas membrane
Supplier assessment
• Aluminium foil membranes are often claimed by sales people to be the “Rolls Royce” or “top of the list” of gas or vapour membranes and better than other types
• They are not – many are extremely thin and prone to damage • Supplier of an aluminium foil membrane
▫ “We do not need VOC permeation test data because we have a layer of aluminium”
• Foil can be as thin as 12 microns (0.012mm thick) • It has pinholes through it from manufacture that will allow
vapour to migrate through it • Therefore you need test data as per CIRIA Report C748
Membranes • Check actual properties – sample on site? • Sample of aluminium foil gas membrane
taken from site • Tested at an independent laboratory
Property Claimed on data sheet
Measured values
BS8485: 2015 min
requirements Thickness at reinforcement (mm)
0.4 Not stated where it is measured
0.44 to 0.51 Mean 0.46
(1811 gauge)
--
Thickness in between reinforcement (mm)
Not stated 0.32 to 0.35 Mean 0.33
(1299 gauge)
0.4
Mass per unit area (g/m2)
370 343 to 355 Mean 349
370
Membranes
• It does not meet the minimum requirements from BS8485: 2015
• Ground gas handbook – use minimum 2000g membranes
• Thickness of plastic sheet protecting the critical foil is 0.33mm / 2 = 0.165mm (650 gauge)
• Small nicks and tears in plastic expose aluminium to cement paste if below slabs or screed directly on top – alkaline and corrodes the aluminium
• Membrane needed to prevent cement bleeding and reaching foil membrane!
Exposure to concrete
• Slight tear that is commonly seen on site (actually not as bad as some damage seen just from foot traffic let alone steel fixing)
Practical implications
• C748 places emphasis on robustness, chemical resistance as well as testing of permeation rates
• Thin foil membranes are not robust or durable enough to act as VOC membranes
BBA certificates
Which one would you have most confidence in?
1. VOC membrane with a BBA certificate
2. VOC membrane without a BBA certificate
BBA Certificate membrane
• Certificate states “the product is chemically resistant when exposed to, and limits the transmission of, volatile organic compounds (VOCs)”
• “Buildings in areas at risk of VOCs should follow the guidance detailed in CIRIA C748”
• BUT • Permeation test data is not in accordance with ISO 15105-02 as
recommended in C748 • Permeation test data limited to toluene and xylene (also diesel and petrol) • Permeation test is a liquid permeation test • Durability testing is not in accordance with C748 • Indicates joints can be taped but then states: • “The butyl tape has limited resistance to diesel and similar materials.
Welded joints must be used where there is any doubt over the compatibility of butyl tape”
Non BBA membrane
• Permeation test data in accordance with C748 with laboratory test results available
• Permeation coefficients provided
• Durability test data in accordance with C748
• Welded joints not affected by VOCs
• Resistant to puncture and tear • JUTA GP Titan • Proctor VOC Flex
Comparison of permeation rates
Can membranes solve everything?
• VOC membranes are not the solution to all problems
• NAPL at 0.65m – allowable concentrations exceeded even with a membrane and void with standard ventilation
• Could increase ventilation ? • But should we really be
leaving NAPL at shallow depth below housing sites?
• Consider concentrations in the void – odour issues at air bricks?
Permeation rates
• Ask to see laboratory test results • If nothing to hide a supplier will provide the test certificates and
graphs • Has testing continued to breakthrough?
Continuous internal monitoring - VOCs
• Often the primary contaminants of concern in VOC assessments are BTEX and chlorinated solvents PCE, TCE, DCE and vinyl chloride.
• Extremely low residential indoor air quality targets for these contaminants (particularly the chlorinated solvents)
• Requires ppb level instrument (can also change lamp voltage to target more specific range of VOCs)
• Sampling and analysis also requires very low MDLs - using a lab from the USA who are able to achieve lower MDLs than the UK labs.
• ppm monitor is unlikely to measure VOCs at a site where the risk is borderline. It may however provide useful information at a high risk site for in ground monitoring
• Understanding internal sources is critical with lower limits of detection
RfCs for various VOCs
Compound Mol Wt. RfC
(ug/m3) Concentration
(ppb) Concentration
(ppm)
Benzene 78.11 5 1.5 0.0015
Toluene 92.14 5000 1302.4 1.3024
Ethylbenzene 106.16 260 58.8 0.0588
Xylene 106.16 200 45.2 0.0452
Naphthalene 128.17 30 5.6 0.0056
Tetrachloroethylene (PCE) 165.83 40 5.8 0.0058
Trichloroethylene (TCE) 131.39 2 0.4 0.0004
Cis 1,2-dichloroethylene 96.94 0.27 0.1 0.0001
Vinyl chloride 62.5 1 0.4 0.0004
1,1,1-trichloroethane (TCA) 133.41 380 68.4 0.0684
1,1-dichloroethane 98.96 5 1.2 0.0012
1,2-dichloroethane 98.96 0.4 0.1 0.0001
1,1-dichloroethylene (DCE) 96.94 5 1.2 0.0012
Groundwater or vapour assessment?
• Consider the CSM (again!)
Final thoughts • The key to successful VOC risk assessment is choosing the most
appropriate ground model and building parameters • VOC membranes need to be critically assessed to make sure the risk
is mitigated to an acceptable level • Critically assess VOC membrane properties especially those relating to
durability • Use ppb level instruments for internal or underfloor void VOC
monitoring • For basements consider whether the VOC hazard is from vapour or
groundwater ingress
Thank You
Contact: [email protected]