Wednesday, December 12, 2018

Simple Techniques for Assessing Airflow in Occupied Spaces

Jeff Burton is a treasure to our profession.  He wrote a piece on ventilation earlier this year and published it in the AIHA Synergist.  I found it to be incredibly valuable.  On the chance that you did not see it, I am reproducing part of it below with his permission.  It is a trove of practical advice born from a lifetime of experience  and a great resource for any practising IH.

One thing the Jeff did not mention but that I think is important is that much of this can be used for exposure modelling input.

I am reproducing the first few paragraph of the article below.  If you are a member of AIHA, you can go to the online version in the Synergist to get it in all its glory at:

If you are not a member, and you want it for your personal use, you can send me a request ( and I will send you the original MS Word document that Jeff sent to me. 


Six Ways to Approximate Airflow

Simple Techniques for Assessing Airflow in Occupied Spaces

By D. Jeff Burton

Every occupational health and safety professional must be able to evaluate the air the occupants of a space are experiencing to assess the potential for IAQ problems and their solutions.

Most OHS professionals today are unable to conduct in-depth testing or measurement of HVAC systems and their airflows. Specialized knowledge of testing, measurement, and balancing is often required on the complex systems of today. Industrial hygiene engineers or TAB (testing, adjusting, and balancing) specialists can be employed to make detailed measurements. However, an OHS professional can often gather enough simple information to quickly provide approximate answers to questions about airflow in a space, regardless of the complexity of the system.

This article provides guidelines for simple testing, measurements, and approximations an OHS professional might perform. These include temperature and humidity; air movement and distribution, outdoor air flowrates, and air exchange rates in the occupied space; concentrations of carbon dioxide in the air; and the effects of wind on the airflow through a building.

The following equipment is needed to perform the simple tests and measurements described in this article: tape measure, thermometer, psychrometer, smoke tubes, and carbon dioxide monitor.


Are REACH Exposure Models Good Enough?

The political will in the European Union to enact REACh was and is extraordinary.   The body politic in the EU wants this regulation and certainly needs it to be effective. It should be clear that it cannot be effective if the exposure assessment half of the risk equation used for REACh is faulty.  Underestimation of exposure and risk hurts people's health directly, over-estimations hurts people's well-being by unnecessary hurting of the economy.   The use of good modelling tools is critical or REACh, in my opinion, will ultimately be doomed to fail. 

I have always thought that first principle physical chemical models (FPModels) have been superior to models that are not based on first principles (NFPModels).  Now a thoughtful and talented Danish researcher (Dr. Antti Joonas Koivisto) is examining and demonstrating with logic and DATA exactly why first principle models are better and, most likely, even necessary to make good regulatory decisions.

An early question might be:  Why develop NFPModels when FPModels are available for development?   The easy and probably correct answer:  They can be developed relatively quickly and with less effort and expense. FPModels are available but need to be parameterized for critical exposure scenarios and that means research dollars.

NFPModels, for the most part, are based on dimensionless factors to calculate scores, which are then converted to exposure values.  They are conceptual models than do not have to conform to first-principles and are thus (using Joonas' word) somewhat vague.

While there are other NFPModels, the big hitter in the EU for modelling exposure via REACh appears to be Stoffenmanager® v.7.1 which as of last month:

·         is reportedly validated by 15 scientific studies based on more than 6000 measurements. 
·         has more than 33,000 users with 50 new users per week. 
·         used to make over 200,000 regulatory decisions

It is accepted by the Dutch Labour inspectorate as a validated method to evaluate exposure to hazardous substances in the workplace.   More important, the European Commission officially recognises Stoffenmanager as a instrument to comply with the REACh regulation.

Other REACh-recommended NFPModels include:


Although somewhat varied in their approach, they all share the same feature that they are
all based on dimensionless factors to calculate scores, which are then converted to exposure values.  They are conceptual models than do not have to conform to first-principles (like the conservation of mass).  Thus, they are not scientifically formalized and that leaves them difficult to explain.

Dr. Koivisto asserts, and I agree, that there should be minimum requirements for regulatory exposure models and that those criteria should be no less than the Daubert criteria used in US Courts for valid scientific testimony.  The model criteria: 
  •          Is applicable and has been tested.
  •          Has been subjected to peer review and is generally accepted.
  •          The rate of error is known and acceptable.
  •          The existence and maintenance of standards and controls concerning the                     operation.
  •          Is generally accepted in the relevant scientific community.
Joonas goes on to advise that FPMmodels are superior to the above NFPModels (what he calls “imaginary” models) because:

       Mass flows are traceable à Model can be used for environmental, occupational and consumer exposure assessment!!
       There is No unit conversions!!
       Error analysis can be made separately for emission source, emission controls, and dispersion.
       No need for Tier levels;  the Tier level depends on available information.
       Possible ”calibration” is straight forward (e.g. chamber tests)
       In the NF/FF model the NF volume and air mixing are adjustable according to the source (free parameterization).
       Results are easy to interpret
       Easy to develop for further needs
       No need to discretize parameters (e.g. room size, ventilation rate,…)
       Accuracy superior when compared to compared to mechanistic or conceptual modes

I took most of the above from a November 29, 2018 presentation that Joonas gave in Denmark.  I will be happy to send the PowerPoint slide deck of that talk to anyone who asks at

Wednesday, September 12, 2018

IH Mod 2.0 - A Major Advance in Exposure Modelling Tools

I have not blogged for quite a while primarily because in 125 blogs I pretty much exhausted what I wanted to say on various topics.  Also, new ideas for blogs from the readers also seemed to have dried up.  I am, however, moved to post again by the wonderful work of Daniel Drolet and Tom Armstrong on the tool many of us know as IH Mod.  For years, they have wanted to combine the power of these deterministic models with the new dimension of stochastic uncertainty modelling (e.g., Monte Carlo simulation).  Daniel is a brilliant programmer and he made it happen!  It is now available as IH Mod 2.0 and, as usual, its a free download.  Daniel and Tom and all the folks who worked on this have done so without pay for the benefit of the professional.  Below is Tom's announcement.   I remain open at for ideas for future blogs.   I do have another blog that will come out soon with goodies from Jeff Burton and the wonderful tools on ventilation he has recently provided to the profession.

Attention all exposure assessors who use or want to use mathematical modeling to estimate airborne exposure to chemicals!   IH Mod 2.0 and a Support File are now available (on the public access Exposure Assessment Strategies Committee web page.

IH Mod 2.0 includes the same mathematical models as in the still available original IH Mod.   IH Mod 2.0 gives the user the choice between running the models in deterministic (point value parameters) or in Monte Carlo Simulation mode, with choices of distributions of parameter values.  This is right in MS Excel with no other software needed.  It requires a desktop install of MS Excel,  for  Windows or Apple computers.  The currently posted version has English, French, Serbo-Croation and Japanese language options.  Spanish, German and Italian will be available soon.

Support File for IH Mod 2.0 is also available.  It includes useful information about IH Mod 2.0, and spreadsheet tabs to estimate liquid spill pool generation rates via the Hummel-Fehrenbacher equation, a units of measure conversion tool, examples of generation rate estimation, a "Bootstrap" procedure tool, a summary of approaches to estimate ALPHA for the exponentially decreasing emission rate models, and some links to other resources.  The support file is evolving and will be updated periodically with new information.  Check back at the EASC web page (URL above) for updates.