Ask the Expert

Confessions of a Certified Industrial Hygienist (CIH) Examinee interviews recent successful examinees of the Certified Industrial Hygienist (CIH) exam administered by the American Board of Industrial Hygiene (ABIH).  The resultant text is as follows:  When did you decide to take the CIH exam?

Examinee:  I decided in 2003 to make it a goal of mine to obtain the CIH certification.  When did you obtain certification?

Examinee:  I actually obtained certification in May 2010.  What is your current career field and how do you feel it prepared you?

Examinee:  Currently I am in the consulting field.  I feel that it (i.e. being a consultant) prepared me by having the ability to complete a multitude of traditional IH projects.  The great thing about being a consultant is that there is always something new and fresh in meeting the needs of the client, which exposes you to a variety of the traditional “IH rubrics”.  How long had you been in the IH/Safety career field when you sat for the CIH exam?

Examinee:  Less than 10 years.  I believe it was actually 9 years.  While you can take the test after 5 years, I have always personally regarded the CIH designation highly.  I felt that it was important and wanted to have a certain “skillset” prior to sitting for the exam.  Are you saying that you did not just want to have a “certification” but wanted to be able to exemplify the characteristics of most CIH’s in the field?

Examinee:  Exactly.  That is precisely my thoughts and feelings.  What was/is your work/career-life like?

Examinee:  I consider myself very fortunate to have a very well qualified mentor (who is a CIH) and excellent IH support staff around me.  Personally, I feel that it would have been much more difficult to obtain such a high level IH skillset without those continuing resources.  Personally, how many hours do you think you studied in preparation for the CIH exam?

Examinee:  Great question.  But one that I thought about many times after many months of studying.  I’d imagine that I studied somewhere in the range of 700-800 hours in all.  Granted, this was over a few years.  However, over the final year leading up to the exam, the final breakdown was probably somewhere in the range of:

  • > 12 months out = 120 hours
  • 12 – 6 months out = 200 hours
  • 6  – 3 months out = 200 hours
  • 3 – 1 months out = 120 hours
  • < 1 month out = 60-90 hours


Ask the Expert: Ventilation and Fan Requirements

Ask the ExpertD. Jeff Burton, PE, CIH, noted author and OH&S contributor, lends a hand on this “Ask the Expert” question.

Q: How do I go about taking measurements for an old, underperforming laboratory fan for specification of a new fan?

A: When specifying a fan, the two basic numbers you need are Q and SP — called the “System Operating Point,” SOP.

There are two ways of determining “SP.” According to AMCA , one is the Fan Total Pressure (FTP) and the other is Fan Static Pressure (FSP).

FTP represents all energy requirements for moving air through the ventilation system. FTP is calculated by adding the absolute values of the average total pressures found at the fan. If the normal sign convention is followed, then a formula for FTP is:

FTP = TPoutlet – TPinlet

substituting for TP gives

FTP = SPout + VPout – SPin – VPin

If VPout equals VPin, i.e., if the average inlet and outlet velocities are equal, then the VP terms in the above equation cancel, leaving:

FTP = SPoutlet – SPinlet

The fan static pressure (FSP) is defined as the fan total pressure minus the average velocity pressure out of the fan.

FSP = Fan TP – VPout

(The fan static pressure is not defined as the static pressure out minus the static pressure in.)

Substituting the value of FTP into the FSP equation:

FSP = SPout + VPout – SPin – VPin – VPout

The VP (out) terms cancel, leaving

FSP = SPout – SPin – VPin

FSP represents the system losses, i.e., the amount of static pressure converted to useless heat or noise. (more…)

Ask the Expert: Low Noise Attenuation Earplugs


Ask the Expert:  Elliott Berger, author and editor of The Noise Manual (available at AIHA press or Amazon), recently commented on the use of low attenuation ear plugs for use in industry on the Yahoo Groups AIHA listserv.

In looking over recent posts on low-attenuation earplugs I was pleased to see awareness of the issue of over protection. The E-A-R Hi-Fi earplug was mentioned and indeed that is one moderately priced alternative to obtain less attenuation and a more neutral attenuation characteristic that sounds more natural. Unfortunately there are limited choices in this regard today since there isn’t much pull through from the occupational community. In fact, 3M used to sell the Hi-Fi earplug in the industrial market at the UltraTech (and still does in Europe), but in the US there is so much emphasis on high NRRs that it was difficult to garner interest. Today you can find them at various online retailers.

Another excellent uniform attenuation/moderate attenuation hearing protector, in fact the ultimate embodiment of that style is the Etymotic ER-15 Musician’s earplug. It is truly exceptional but will set you back about $150 per pair. It is cost justified for certain occupations such as musicians where the best fidelity is required. Go to to learn more.

To learn more about the effects of HPDs on communications see EARLog 13 found here:

Elliott H. Berger
Senior Scientist, Auditory Research
3M Occupational Health & Environmental Safety Division
7911 Zionsville Road
Indianapolis, IN 46268-1657
317-692-3031 w
866-428-3942 f
317-752-0614 c

Courtesy of Elliott Berger