Predicting Exposures - Part I

Predicting Exposures I and II

Location – (Web PDC)

Instructions regarding how to log onto the web PDC and the conference call phone number, as well as handouts, will emailed to the registered participants the week before the PDC.


Paul Hewett Ph.D. CIH

Course Description

These web PDC introduce the participant to the prediction of occupational (or consumer) exposures using Well Mixed Room (WMR), Constant Emission models.  Modeling software (Windows only) will be provided that is capable of Monte Carlo Simulations resulting in the prediction of an exposure profile.  This PDC will concentrate on the practical application of WMR models to several exposure scenarios.  Participants are encouraged to bring modeling examples.

Each PDC will last 3.0 hours, with an additional 30 minutes for Q&A.  Each participant will receive a certificate confirming participation in the PDC.

To assist the student, EAS Inc. will provide a student version of the the Task Exposure Assessment Simulator (TEAS) program.

Learning Objectives

Upon completion, participants will be familiar with …

Part I

  • Selecting an appropriate Well Mixed-room (WMR) Constant Emission model.
  • Using a hand-calculator to calculate the TWA for a task or series of tasks.
  • Using the provided student software to describe a job as a series of WMR modeled tasks.
  • Predicting exposure profiles using Monte Carlo Simulation.
  • Calibration of a WMR model using field measurements and/or default values.

Part II

  • Selection of an appropriate Well Mixed-room (WMR) Decreasing Emission model.
  • Using a WMR model to predict short-term (i.e., 15-minute) and peak exposures.
  • Selection and use of appropriate generation rate prediction algorithm.
  • Estimating the potential benefit of using a local ventilation control.
  • Predicting vapor concentrations immediately after a workplace spill.


  • Familiarity with the AIHA Exposure Assessment and Management Model (see the AIHA monograph “A Strategy for Assessing and Managing Occupational Exposures”, 4rd Edition (2015)

Recommended Reading

  • Hewett, P. (2017): Easy Modeling – Forecasting Occupational Exposures Using “Well Mixed Room” Models. Synergist (April) 24-29.
  • Hewett, P. and Ganser, G.H. (2017): Models for Nearly Every Occasion: Part I – One Box Models. Journal of Occupational and Environmental Hygiene 14:49-57.
  • Ganser, G.H. and Hewett, P. (2017): Models for Nearly Every Occasion: Part II – Two Box Models. Journal of Occupational and Environmental Hygiene 14:58-71.
  • Nicas, M. and Armstrong, T.W. (2015): Appendix I – Estimating Airborne Exposure by Mathematical Modeling. In A Strategy for Assessing and Managing Occupational Exposures. (editors: Jahn, S.D., Bullock, W.H., and Ignacio, J.S.) American Industrial Hygiene Association, Fairfax, VA.

Presentation List

Part I

  • Introduction to WMR models (including the new models introduced by Hewett and Ganser)
  • Deterministic and Probabilistic Modeling
  • Use of the Modeling Software
  • Model Calibration and Validation
  • WMR Model Prediction Accuracy, Advantages, and Limitations
  • Group Workshop
  • Stump the Instructor: Evaluation of Student Exposure Scenarios
  • Q&A

Part II

  • Introduction to WMR Decreasing Emission models (used for evaporation scenarios)
  • Introduction to Generation Rate Prediction Algorithms
  • Comparing Control Options
  • WMR Modeling and Workplace Spills
  • Discussion of WMR Modeling Research Needs
  • Stump the Instructor: Evaluation of Student Exposure Scenarios
  • Q&A


See Registration page.

Cancellation Policy

See Registration page.

Read these notes before you sign up:

NOTE: The registration and participation policy for each Web PDC is the same as for a fixed location or on-site PDC. Registration is per participant, not per viewing site. Each participant must register.  Only those registered should view and participant in this web PDC.

NOTE: The email address submitted at the time of payment will be used for all email communications and for logging onto the web PDC.

NOTE: This web PDC will presented using GoToMeeting. GoToMeeting must be installed on your computer. To install (usually takes less than two minutes), click on the GoToMeeting link above, scroll to the bottom of the page, and click on the link “Download GoToMeeting (for customers)”. If you do not have administrative privileges for your computer have your IT person install the GoToMeeting software at least the day before the web PDC.

NOTE: The conference call number will not be toll free. You will be responsible for any long distance phone charges if you do not have an unlimited long distance account. However, you may also connect using your computer speakers and microphone or headset (VoIP).

NOTE: See the “Prerequisites” below for software and freeware that will be helpful when taking this web PDC. To download and install the program(s) you must first be a registered member of