Asbestos Abatement (C-22) · Lesson 1 of 5

Sizing Negative Air Units: Enclosure Volume, ACH, and CFM

"Sizing Negative Air Units: Enclosure Volume, ACH, and CFM" is lesson 1 of 5 in the Asbestos Abatement (C-22) Learning Hub. It opens with "What the Rule Requires" and works through 5 short steps, then a worked example you can check yourself against.

Open the free trialSee pricing

One-time purchase, no subscription. Law & Business included.

Steps in this lesson

  1. What the Rule Requires
  2. Get the Enclosure Volume
  3. The CFM Formula
  4. Turn CFM Into a Number of Machines
  5. Check the Result and Prove It on Site

The worked example in the course applies this lesson to a realistic job in 7 steps, from "Required airflow" through "Field proof".

What you'll be able to do

  • Explain the main idea of "Sizing Negative Air Units: Enclosure Volume, ACH, and CFM" in plain language you can use on the exam.
  • Apply this step with confidence: "The CFM Formula".
  • Apply this step with confidence: "Turn CFM Into a Number of Machines".
  • Apply this step with confidence: "Check the Result and Prove It on Site".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Negative Air: 20,000 cu ft Enclosure at 4 ACHPLAN VIEW OF SEALED ENCLOSURE (not to scale)50 ft40 ftNAUNAUMake-up air inCeiling height 10 ft2 NAUs x 1,000 CFM rated = 2,000 CFMManometer: -0.02 in. w.c. or lowerSIZING THE UNITSVolume = 50 x 40 x 10= 20,000 cu ftCFM = V x ACH / 60= 20,000 x 4 / 60 = 1,333 CFMUnits: 1,333 / 1,000 = 1.33Round UP = 2 unitsCheck: 2,000 x 60 / 20,000= 6.0 air changes per hour6.0 ACH delivered ≥ 4 ACH required (1,333 CFM minimum)ENCLOSURE PASSES the airflow checkOne unit alone = 1,000 x 60 / 20,000 = 3.0 ACH, which would FAILSource: 8 CCR 1529(g)(5)(A)1; Purple Book App. J.2.1.2.1 and J.3.1.1 (CFM = volume x ACH / 60)CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What the Rule Requires

Title 8 section 1529(g)(5)(A)1 says a negative pressure enclosure (NPE) must keep at least 4 air changes per hour (item b) and a pressure differential of at least -0.02 column inches of water relative to outside pressure, shown by manometer readings (item c). It must stay under negative pressure for the whole time it is in use (item d), with air movement directed away from the employees doing the work and toward a HEPA filtration or collection device (item e). Sizing the negative air units (NAUs) is how you prove the first number on paper before the machines ever start.

Step 2: Get the Enclosure Volume

EPA's Purple Book, Appendix J.3.1.1, says the work-area volume is the floor area times the ceiling height, in cubic feet. Appendix F to section 1529 adds that the enclosure should be the minimum volume that still covers all the work surfaces and lets workers move and air sweep past them. Measure the barriers you will actually build, not the room on the plan, because a wrong volume carries into every later number.

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.

More lessons for this trade

Browse all lesson previews

Ready to practice for real?

Try the real classroom free, no sign-up, or get the full course for your trade.

Open the free trialSee pricing

Independent exam preparation. Contractors Classroom is not affiliated with the Contractors State License Board, and no course can guarantee a passing result.