Re: maximum permissible limits

["Jerry Cohen" <jjcohen@PRODIGY.NET>]

Ruth,

    I don't think your response really addresses Franz's query. The

determination of whether "maximum permissible" exposures are exceeded

would require only a one-sided (high end) evaluation. In determining whether

a speed limit is exceeded, it is not necessary to test how slow the vehicle

might have been going.

    The problem in evaluating compliance with MPC criteria lies in the fact

that exposure levels are not uniform and generally vary  stochastically

(both spatially and temporally). Any single measurement gives only the

ambient concentration for one given location and time period.

A series of measurements will  show various results. Since exposure

levels vary stochastically, there will always be some finite (non-zero)

possibility

that MPC levels might have been exceeded. Whether that possibility must be

below the 1, 2, 3, 5 , 10 or whatever sigma level to be "acceptable" has not

been addressed.

    When exposure limits (MPC's,  TLV's, etc) were originally

conceived, they were intended to provide guidance for the professional

judgment of industrial hygienists, health physicists, and other health

professionals. They were not intended to be rigid regulatory limits.

Unfortunately, these guidelines were later codified into laws & regulations

including penalties for exceeding these limits.

    So, getting back to Franz's question, when should exposure limits be

considered violated? When the probability that they might be exceeded is:

0.1, 0.01, 0.001, 0.000001,   or what? One may need to a lawyer, politician,

or theologian to answer that.  I am sure that, provided sufficient funding,

the NCRP would be happy to study the problem and let us know what further

study might be needed to reach a solution.                          Jerry





> >This reason is exactly why statistics profs advise

> >people doing _research_ to use 2-sided confidence

> >limits, and discourage the practice of 1-sided limits

> >in most cases.  [1-sided limits have some valid

> >applications in non-research fields such as quality

> >control and business management].

>

>

> --------------------------------------------------------------------------

>

> This comment raises for me a very important question: What is the

criterion,

> whether a maximum permissible concentration (MPC) has been exceeded? There

are two

> extremes possible: Is it, that the measured value plus x sigma has to be

> below the MPC or is it that the measured value has to be below the MPC

plus

> x sigma? The latter criterion is used in most regulations in Austria

> regarding contaminants in food (x=2). The criterion defined by the

Austrian

> Standardisation Organisation (which has to be regarded as a recommendation

> and has no real legislative power) is coherent with the first extreme. I

> wonder, what the legislation is in other countries.

>

> Best regards,

>

> Franz

> #

>

>









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