Whole Air Samples Near the Breathing Zone without Using Pumps

Advantages for using Whole Air Sampling?

• Easy 
  
• No Pumps 
• No Batteries 
• No Selection of Media 
• Compatible with Hundreds of Compounds 
• No Matrix Concerns. Multiple analytes OK 
• No Humidity or Temperature Concerns 
• No Breakthrough / Recovery Concerns 
• No Analytical Chemistry in the Field 
• No Solvents needed in the Laboratory
  

Whole Air Sampling Problem

How do we get people to wear these?

US OSHA PV2120-2002

• 400cc vacuum canister worn around waste 
• Flow Controller to Fill at a Constant Rate from 15 minutes to over 8 hours 
• Sample line brought to the breathing zone 
• Monitoring of compounds from PPM to 1 PPBv
•  Starting to fail the “Simple” criteria

How much whole air do we need to Collect and Analyze?

How Small can we make our Canisters?

MDL (GC/FID or GCMS)

• 0.4 PPM
• 0.04 PPM 
• 0.004 PPM

Air Sample Volume

• 0.1cc
• 1cc
• 10cc

A 50cc Canister is all we need. 

 How do we fill it over an 8 hour period???

Solution - Using Helium as a Pump 

• Canisters are Filled with Helium instead of being evacuated 
• The canister is opened, and helium starts to diffuse out 
• The resulting loss of helium creates a vacuum that pulls the sample into the canister
  

Helium Diffusion Sampling

Changing the size of the diffusion zone (diameter and length) changed the sampling rates

Fill Times from 15 minutes to 8 hours were achieved

Fill rates were nearly constant over the first 40% of exchange

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8 HR

4 HR

2 HR

1 HR

15 Min

Helium is Slowly Replaced by Air Sampling is Constant for up to 40% Helium/Air Exchange

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Collecting an HDS Sample in the Field

• Verify positive helium pressure to prove no contamination has occurred 
• HDS Monitor placed near breathing zone 
• Remove valve and store in pouch 
• Replace valve after monitoring period (15 min to 8 hours) 
• Record Sampling time, duration, location, subject name, etc 
• Send to lab for analysis

Determine the amount of Sample Collected by Weight Gain

• Weighting the sample in the lab determines the amount of air sampled 
• Direct measurement of volume of air sampled is not possible with other diffusive monitors

Molecular Wt Air (10% RH) =28.94 

Molecular Wt Air (50% RH) = 28.81 (+-0.4%) 

Molecular Wt Air (90% RH) = 28.65 

(Wt Sample – Wt Helium) 

%Air in Canister = ---------------------------------- X 100% 

 (Wt Air – Wt Helium)

(Wt Sample – 1/7.20 x Wt Air)

 %Air in Canister = ---------------------------------- X 100% 

(Wt Air – 1/7.20 x Wt Air)

Ratio Air (50% RH)/Helium = 28.81/4 = 7.20 

 Substituting Wt Helium = 1/7.20 Wt Air

Calculating Weight Gain & Sampled Amt

A simple spreadsheet is available for calculating weight gain \

Simply adjust the pressure of each sample that comes into 15 psia with helium prior to weighing 

Then evacuate the sampler after analysis and reweigh it to determine % Air collected.

2 m/sec Face Velocity

Same

Same

10% 

Increase

Benzene

Toluene

Et-B

o-Xylene

m,p-Xylene

• Silonite coated 6L Chamber used to create 1PPM stable test mixture 
• 4 HDS Monitors were challenged simultaneously (4 15min and 4 8Hr Monitors) 
• A 50cc vacuum container collected a sample at the end that was used as 100% to calibrate the GCMS

Recovery of 39 Light to Heavy VOCs at 1PPM Each

• No significant differences were observed in sampling rates of compounds from molecular weight of 50 to 256 g/mole. 
• Although Helium loss is controlled by diffusion, the sampling rate data shows that chemicals in air are actively sampled

To Prep for Monitoring– Fill/Evac again, then one final fill with Helium to 3-8 psig, and it’s ready for another sampling event

Monitors can perform hundreds of samplings

To Clean – Evac/Fill once, pull a vacuum, remove and oven bake

• “Maximum allowed” exposure testing 
• Uses 15 Min HDS Monitor but with a vacuum instead of Helium to collect a sample in 2-3 seconds 
• No other sampler collects samples “instantly” 
• Measures hundreds of compounds for which there are no real-time chemical sensors

New Ceiling Measurement OSHA Method Nearing Completion

Official Method should be released later this year

Elimination of adsorbents and the variations they produced from sampler to sampler greatly improves method consistency

OSHA has confirmed the combined “Sampling Rate Variation” + “Analytical Method Variation” is only 3-5%, making it one of the most accurate OSHA methods ever developed

Helium Diffusive Sampling - Conclusion

• A Whole Air Sampling alternative to adsorptive sampling has been presented 
• Slower sampling rates are possible by using Helium diffusion out of the canister, allowing smaller canisters to be used while eliminating external flow controllers 
• Weight measurements confirm the actual amount sampled, improving the reliability over samplers that cannot prove volume collected
• Since this is vacuum sampling using a self-contained helium pump, this is just another way of performing US EPA Method TO15 
• Allows a very wide range of compounds to be recovered with no adsorbents 
• Laboratory measurements to 0.1 PPM with no Preconcentration, or 0.002 PPM by preconcentrating 20cc

Dan Cardin, Pat Stefani, Daniel Cardin, Tom Robinson

• Mike Simmons, OSHA Salt Lake City, UT USA 
• Tom Massoin, ALS Analytical Laboratory, Salt Lake City, UT USA 
• Professor Brent Olive, Northern Alabama University, AL USA 
• HDS Development Engineers and Chemists, Simi Valley, CA, USA

We would love to hear from you! Please let us know if you have any inquiries 

Email:

[email protected]

Phone:

805-527-5939

2207 Agate Ct. 

Simi Valley, CA 93065