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Calcimator

PEL Compliance Calculator

Calculate Time-Weighted Average (TWA) exposure and compare against the OSHA Permissible Exposure Limit to assess compliance.

Inputs

Results

8-hr TWA

36.25

Exposure ratio (%)72.5%
Total sampled hours8
Action level (50% PEL)25
Status (0=OK, 1=Action, 2=Over)1
Max remaining conc.0
Avg Conc36.25
How to Use This Calculator
  1. Enter OSHA PEL (ppm or mg/m³), Segment 1 concentration, and Segment 1 duration (hrs).
  2. Set Segment 2 concentration, Segment 2 duration (hrs), and Segment 3 concentration.
  3. Adjust Segment 3 duration (hrs), Segment 4 concentration as needed.
  4. Review the 8-hr TWA result.
  5. Use Exposure ratio (%) and Total sampled hours to inform your decision.

How the result changes with Segment 2 concentration

Segment 2 concentration8-hr TWA
10,0003,763.75
35,00013,138.75
65,00024,388.75
90,00033,763.75

What each input means

OSHA PEL (ppm or mg/m³)
The Permissible Exposure Limit for the substance (e.g. 50 ppm for acetone).
Segment 1 concentration
Measured or estimated airborne concentration during segment 1.
Segment 1 duration (hrs)
Hours of exposure at segment 1 concentration.
Segment 2 concentration
Measured or estimated airborne concentration during segment 2.
Segment 2 duration (hrs)
Hours of exposure at segment 2 concentration.
Segment 3 concentration
Measured or estimated airborne concentration during segment 3.
Segment 3 duration (hrs)
Hours of exposure at segment 3 concentration.
Segment 4 concentration
Measured or estimated airborne concentration during segment 4.
Segment 4 duration (hrs)
Hours of exposure at segment 4 concentration.

What each result means

8-hr TWA
Time-Weighted Average exposure normalised to an 8-hour workday: Σ(C×T)/8.
Exposure ratio (%)
TWA as a percentage of the PEL. Over 100% means overexposure.
Total sampled hours
Sum of all segment durations.
Action level (50% PEL)
Concentration at which medical surveillance and monitoring are triggered.
Status (0=OK, 1=Action, 2=Over)
0 = below action level, 1 = above action level but below PEL, 2 = above PEL.
Max remaining conc.
Maximum average concentration allowed for remaining shift hours to stay at PEL.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    OSHA PEL (ppm or mg/m³) = 50, Segment 1 concentration = 30, Segment 1 duration (hrs) = 2, Segment 2 concentration = 60 = 9 input(s) provided
  2. Calculate 8-hr TWA
    36.25 = 36.25
  3. Calculate Exposure ratio
    Exposure ratio = exposureRatio * 100
    72.5 = 72.5
  4. Calculate Total sampled hours
    Total sampled hours = t1 + t2 + t3 + t4
    8 = 8

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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