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Sunday, January 26, 2014

IH’s Dirty Little Secret


Blogging is a remarkable media; indeed, this blog has opened communication among colleagues in a manner that I did not anticipate.  This week’s blog represents a prime example.

You may remember that two of the last three blogs deal with the subject of sampling statistics in which I tried to make the point that exposure is naturally quite variable and that by just taking one or a few samples, we can be tricked as to whether a workplace is really in compliance relative to an OEL.  The blogs advocated using good statistical software such as IH STAT to help interpret the data. 

In response to these blogs I heard from a respected colleague who has a lot more field experience as an IH than I do.   Indeed, I would describe him as a seasoned and very thoughtful exposure assessor.   Because he does not want to jeopardize his future employment opportunities he has asked that I keep his comments anonymous which I am pasting below: 

“I think that the AIHA as an association has failed to a great degree to educate industry about this particular failing of our profession [the severe limitations of small sample size].  I'm not aware of a single piece that has ever been produced that attempts to educate the layperson (most business owners are) about the limitations of small sample sets.  

I also think that a pertinent question has been missed by the IH community.  That is - a reality-based question:  would a chemical-handling business be better off by having a professional IH visit and observe their processes, and conduct a single sample vs. no visit at all?  I have lost sleep over this.  Having worked with hundreds of small (and medium, large) businesses over the years, I recognized this issue soon after attending my first continuing education course on statistics back in the early '90s.

The reality is that a sizable proportion of chemical handling businesses will NEVER find their way to taking ANY samples.   Of the ones that do, VERY FEW would ever entertain the idea of repeat sampling.  This bothered me so much, that for a while I started giving proposals to clients with an explanation of my own regarding statistical limitations, and providing them two options in proposals - one with a single visit/sampling event, a second (obviously more expensive) option that would provide more confidence in conclusions reached - and leave the decision with them. Maybe I'm not a very concise scientific communicator, or just not a good salesman, but NONE of them ever opted for the multiple sampling option.

Another issue addresses a level playing field for consultants. This is really important because if you look at the demographics of the AIHA, consultants are the single largest group, and likely perform more than half of all exposure assessments. If I were to immediately insist that my new customers only go the repetitive sampling route, I would be out of business as a consultant tomorrow.  There will always be someone else to step in that gives the customer what they want. Luckily, my larger, more sophisticated clients will opt for building data validation over time through repeated sampling events, but they are still few and far between.

Lastly, and sadly – OSHA regulations simply don’t address the issue adequately.  Other than a few of the substance specific regulations for repeat sampling, there is no legal impetus for employers to provide a statistically sound approach to exposure assessment.

Hey - thanks for letting me spout off!  This is truly the 'dirty little secret' of the IH field, and in my opinion - no amount of shaming is going to solve this.” 

I appreciate this expression of opinion and truth and I know this person enough to believe he is correct.

From my perspective, I believe that taking one sample is MUCH better than taking none as long as you attempt to factor in the very large uncertainty associated with such action.   Assuming that a geometric standard deviation of about 2 is typical for workplace exposures, then, in my opinion, a single sample value that comes out to be less than 10% of an OEL is a pretty good indication that the average exposure will be below the OEL at least 90-95% of the time.  If true, OEL/10 could become the new action level for single samples.   Indeed, I would love to have some sharp statistical minds to look over this suggested approach and comment.

Another way of appropriately using but a single sample is to be sure you monitor reasonable worst case.  That is, if possible, be sure that your single sample is capturing reasonably foreseeable worst case.  Such factors as maximum product rate and/or minimum ventilation rate would be examples of this approach. 

My sense of all of this is that it seems to point directly to the value of modeling in determining actually what scenarios and conditions should be monitored using our precious resources. 



8 comments:

  1. Mike, while I TOTALLY agree that this is perhaps the most significant issue facing IH consultants and chemical end-users alike, I feel that it's hardly a dirty little secret. It's more like the white elephant in the room.

    Having worked in the environmental lab industry for 20+ years following my stint as an IH technician, it is clear that there is an significant contingent out there whose highest priority is staying within budget. If they can get the most "accurate" result, that's nice, but it's bottom line or bust.

    The only recourse for professionals on the IH or analytical end is to flood our reports with disclaimers, stating the limitations on the data representation regarding the hazards (or lack of) in their workplace.

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  2. Here's a thought, set PELs as the upper confidence limit. Oh, forgot, non-starter.

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  3. This comment has been removed by the author.

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  4. Bert Hakkinen who I have known for many years sent me the following free document on exposure assessment that he thought might be useful to the IH community. I am pasting the information below:

    http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=15263#Download

    3. Planning an Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
    3.1. Purpose of the Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
    3.1.1. Using Exposure Assessments in Risk Assessment . . . . . . . . . . . . . . . . . . 33
    3.1.2. Using Exposure Assessments for Status and Trends . . . . . . . . . . . . . . . . 34
    3.1.3. Using Exposure Assessments in Epidemiologic Studies . . . . . . . . . . . . . 35
    3.2. Scope of the Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
    3.3. Level of Detail of the Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
    3.4. Determining the Approach for the Exposure Assessment . . . . . . . . . . . . . . . . . . . . 36
    3.5. Establishing the Exposure Assessment Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
    3.5.1. Planning an Exposure Assessment as Part of a Risk Assessment . . . . . . 38
    iii

    CONTENTS (continued)
    3.5.2. Establishing the Sampling Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
    3.5.2.1. Data Quality Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
    3.5.2.2. Sampling Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
    3.5.2.3. Quality Assurance Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
    3.5.2.4. Background Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
    3.5.2.5. Quality Assurance and Quality Control . . . . . . . . . . . . . . . . . . 43
    3.5.2.6. Quality Assurance and Quality Control for Previously Generated
    Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
    3.5.2.7. Selection and Validation of Analytical Methods . . . . . . . . . . . . 44
    3.5.3. Establishing the Modeling Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

    3.5.3.1.
    Setting the Modeling Study Objectives . . . . . . . . . . . . . . . . . . . 45
    3.5.3.2.
    Characterization and Model Selection . . . . . . . . . . . . . . . . . . . 45
    3.5.3.3.
    Obtaining and Installing the Computer Code . . . . . . . . . . . . . . 46
    3.5.3.4.
    Calibrating and Running the Model . . . . . . . . . . . . . . . . . . . . . 46
    3.5.3.5.
    Model Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
    3.5.4.
    Planning
    an Exposure Assessment to Assess past Exposures . . . . . . . . . 48

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  5. Hello,

    Thank you for this very interesting discussion on the assessment of exposure and minimal sampling.
    For information in France we use the rule prescribed manner tenth OEL: for a group of similar exposure, if the first three results are less than 1/10 of the TLV, then one finds that the OEL is probably never exceeded.

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  6. Mike
    as validation of some of the threads of opinion, I can tell you in strategic planning of Exposure Assessment Strategy Committee activities that I asked AIHA to pull all consultant's in their annual listing who represented themselves to provide exposure assessments. 321 companies/individuals showed up. How many have participated in the string of PDCs development, or otherwise pursued continuous improvement with regards to the promotion of reducing uncertainty? About 8 of them were names on rosters taking classes, or participating within the committee. Other commenters have it right: budget will drive sampling. So we need to REALLY stress STRATEGY discussions in our PDCs, not "go get more samples". By the way for the commenter saying PEL becomes the UCL, I still am faced with a regulator who a) does not apply statistics and b) believes respirators are 100% efficient in use, so that all decisions WITH EACH INDIVIDUAL SAMPLE are black or white against an OEL.

    Regards, Steve Jahn

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  7. Mike
    First, an interesting paper by Clerc and Vincent on this sort of thing was published on advance access three days after your blog. See http://annhyg.oxfordjournals.org/content/early/2014/01/29/annhyg.met084.abstract
    It tends to back up the French procedure referred to above by Anonymous.
    Second, this procedure was also adopted in the guidance produced by the British and Dutch occupational hygiene societies, downloadable from http://www.bohs.org/library/technical-publications/ . It is also in the draft of a European Standard currently under discussion in CEN (although the working group has not yet got to that part of the document). The rationale of the French and BOHS-NVvA approach was described by Jérôme Lavoué and me in a JOEH paper http://www.tandfonline.com/doi/abs/10.1080/15459624.2012.663702#.UuuOGfku98E
    Best wishes
    Trevor

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  8. Absolutely. I was floored when as a young pump jockey with a strong stat background was told by CIH OSHA field officers that 3 - 4 samples was considered statistically representative. Something verified 10 years later by another field office 12 states away. The VP, a CSP, was there at the time and his jaw hit the table. From pers onal experience I collected over 2000 samples on one project using PC XR2s and one can see the significsnt impact of ambient atmospheric changes on the process

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