**Use of Error Factors in Determining a Miner's Overexposure to DPM**

The DPM permissible exposure limit (PEL) is 160 micrograms of total
carbon (TC) per cubic meter of air (160~TC~ µg/m^3^).

1\. TC from a personal sample **must exceed** 160 µg/m^3^ times the
error factor (EF) for TC to result in a miner's overexposure to DPM. The
EF for TC is 1.192. Thus, it follows that the miner **is not**
**overexposed** to DPM when TC from the miner's personal sample **is
less than or equal to** 160 µg/m^3^ times the EF for TC as demonstrated
below:

> TC ≤ 160 x \[EF for TC\]
>
> TC ≤ 160 x 1.192
>
> TC ≤ 190.72

Per MSHA's practice to round up to the next higher integer, 190.72 is
rounded to 191. Therefore, a miner **is not overexposed** to DPM when TC
\< 191 (≤ changed to \< because 191 is greater than 190.72)

2\. When TC from a full-shift personal sample **is** **equal to or
greater** than 191 ug/m^3^, MSHA will evaluate the EC content of the
personal sample as follows to confirm that the TC exposure is not the
result of organic carbon interferences:

The miner **is overexposed** to DPM when EC on the miner's personal
sample for TC is greater than 160 times the EF for EC. The EF for EC is
1.095. This relationship may be expressed mathematically as:

EC \> 160 x \[EF for EC\]

> EC \> 160 x 1.095
>
> EC \> 175.2
>
> 175.2 is rounded up to next higher integer = 176
>
> EC ≥ 176 (\> changed to ≥ because 176 is already higher than 175.2)

Therefore, a miner is overexposed to DPM when EC on the personal sample
equals or is greater than 176 µg/m^3^.

In addition, when the miner's full-shift exposure to EC on the personal
sample is less than 176 ug/m^3^, **an overexposure may still exist** if
the full-shift exposure to EC on the personal sample times the average
TC to EC ratio of one or more area samples is greater than 160 x EF for
TC~adj~.[^1] This may be expressed mathematically as:

> TC~adj~ \> 160 x \[EF for TC~adj~\]

The value of the EF for TC~adj~ depends on the number of area samples
used for determining TC~adj~. This EF ranges from 1.259 when 1 area
sample is used to 1.121 when 10 area samples are used (unlikely we would
ever encounter a situation where more than 10 area samples would be
required - - 1 to 3 area samples would be adequate in the vast majority
of cases). In the following table, the column labeled "citation
threshold" shows the values of 160 times the EF for TC~adj~ for each
case from 1 up to 10 area samples (result rounded to the next higher
integer).

> Number of Area Samples Citation Threshhold
>
> Included in Average TC:EC Ratio for TC~adj~
>
> 1 202
>
> 2 192
>
> 3 187
>
> 4 185
>
> 5 183
>
> 6 182
>
> 7 182
>
> 8 181
>
> 9 180
>
> 10 180
>
> In summary, the miner is overexposed to DPM when EC \< 176 **and**
> TC~adj~ is equal to or greater than the corresponding value from the
> table depending on the number of area samples used. For example, if
> one area sample is used, a miner **is overexposed** when:

EC \< 176

**and**

TC~adj~ ≥ 202

> If three area samples are used, a miner **is overexposed** when:
>
> EC \< 176

**and**

TC~adj~ ≥ 187

[^1]: Multiplying EC on the personal sample by the average TC to EC
    ratio of one or more area samples obtained where non-diesel OC
    interferences are likely to be negligible results in the TC
    concentration of the personal sample without OC interferences. This
    "adjusted" TC value is designated as TC~adj~ to differentiate it
    from TC, which refers to total carbon determined by the ordinary
    method of EC + OC.