Asbestos Abatement (C-22) · Lesson 2 of 5

Air Sampling Math: Turning a PCM Fiber Count Into Fibers per cc

"Air Sampling Math: Turning a PCM Fiber Count Into Fibers per cc" is lesson 2 of 5 in the Asbestos Abatement (C-22) Learning Hub. It opens with "What a PCM Count Measures and What It Is Compared To" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What a PCM Count Measures and What It Is Compared To
  2. Collect the Sample Correctly
  3. Know the Counting Rules the Lab Uses
  4. Do the Calculation
  5. Compare the Answer to the Right Number

The worked example in the course applies this lesson to a realistic job in 7 steps, from "Air volume" through "Clearance side note".

What you'll be able to do

  • Explain the main idea of "Air Sampling Math: Turning a PCM Fiber Count Into Fibers per cc" in plain language you can use on the exam.
  • Apply this step with confidence: "Know the Counting Rules the Lab Uses".
  • Apply this step with confidence: "Do the Calculation".
  • Apply this step with confidence: "Compare the Answer to the Right Number".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
PCM Sample: From Fiber Count to Fibers per ccTHE SAMPLE AND THE COUNTPUMP2.0 L/min25 mmopen-face cassette2.0 L/min x 30 min = 60 Lgraticule fieldFB = 33 fibersFL = 100 fieldsField blanks:BFB = 1, BFL = 200FIBERS PER CCNet = 33/100 - 1/200= 0.325 fibers per fieldAC = Net x 49 / (FR x T)= 0.325 x 49 / (2.0 x 30)= 15.9 / 60= 0.27 f/cc49 = 385 / (1,000 x 0.00785)(filter area / field area)0.27 f/cc < 1.0 f/cc excursion limit (30-minute sample)EXCURSION LIMIT METVolume 60 L is inside the 48 to 100 L guide for a removal with visible dustClass I presumes exposure above the PELs until shown otherwise: respirator stays onSource: 8 CCR 1529 Appendix A (method) and Appendix B 7.1-7.2 (calculation); 1529(c) limitsCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What a PCM Count Measures and What It Is Compared To

Title 8 section 1529(b) defines a fiber as 5 micrometers or longer with a length-to-diameter ratio of at least 3 to 1, and that is what the phase contrast microscope (PCM) analyst counts (Appendix A, item 13). Section 1529(c) sets the permissible exposure limit at 0.1 fiber per cubic centimeter as an 8-hour time-weighted average and the excursion limit at 1.0 fiber per cc over a 30-minute sample, both measured by the Appendix A method or an equivalent. Section 1529(f)(2)(B) tells you that on Class I work you presume exposure is above both limits until monitoring or a negative exposure assessment shows otherwise.

Step 2: Collect the Sample Correctly

Appendix A to section 1529 calls for a new 25-mm cassette with an open-faced 50-mm extension cowl, a flow rate between 0.5 and 2.5 liters per minute, pumps calibrated before and after use, and the sample taken in the employee's breathing zone (items 2, 3, 6, 7). Each set includes 10 percent field blanks or a minimum of 2 (item 11). The non-mandatory Appendix B suggests at least 25 liters for a TWA sample and 48 liters for a 30-minute excursion sample (5.2.7), and no more than about 100 liters where visible dust is present or 240 liters with little dust, to avoid overloading the filter (5.2.8). Air volume is flow rate times minutes.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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