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Activity 002: Ventilation System Performance Assessment

Activity ID: U10M3-ACT-002 Duration: 40 minutes Objective: Assess the performance of a blast cabinet ventilation system using differential pressure readings, capture velocity measurement, and smoke tube visualization.

Overview

Students perform a systematic evaluation of the blast cabinet's local exhaust ventilation system using three complementary methods. This practical assessment builds competency in verifying that engineering controls are functioning as designed.

Materials & Equipment Needed

  • Blast cabinet with dust collector system
  • Differential pressure gauge (installed on dust collector)
  • Smoke tubes (DrΓ€ger CH 25301 or equivalent) with aspirator bulb
  • Velometer or rotating vane anemometer (if available)
  • Tissue paper for quick airflow check
  • Flashlight
  • Data recording worksheet
  • Stopwatch
  • Notepad and pen

Instructions & Procedure

Phase 1: Differential Pressure Assessment (10 minutes)

  1. With dust collector OFF, read the Ξ”P gauge β€” record as baseline (should read near zero)
  2. Turn on dust collector, allow 30 seconds to stabilize
  3. Read Ξ”P gauge β€” record operating value
  4. Compare to manufacturer's specifications:
  5. New filters: typically 0.5–1.5" WC
  6. Change filters when: Ξ”P exceeds 4–6" WC (varies by manufacturer)
  7. Record the filter type, last change date (from maintenance log), and current Ξ”P
  8. Calculate: Is the filter in acceptable range? How much life remains (estimate)?
  9. Document findings on worksheet

Phase 2: Capture Velocity Verification (15 minutes)

  1. Tissue test (qualitative):
  2. With dust collector running, hold tissue paper at each potential leak point:
    • Glove port openings (with hands removed)
    • Door seal perimeter
    • Any panel joints or seams
  3. Tissue should be pulled firmly inward at every point
  4. If tissue is not pulled inward or pushes outward: mark as containment failure

  5. Record pass/fail for each location

  6. Smoke tube test (semi-quantitative):

  7. Crack a smoke tube, attach to aspirator bulb
  8. Slowly squeeze bulb to generate visible smoke stream
  9. Release smoke at each test location (same as tissue test)
  10. Observe smoke behavior:
    • All smoke drawn inward rapidly = good capture
    • Smoke lingers or moves outward = inadequate capture
    • Smoke drawn inward slowly = marginal β€” investigate

  11. Record smoke behavior at each location with sketch on worksheet

  12. Velometer reading (quantitative, if instrument available):

  13. Position velometer probe at the center of the largest cabinet opening (with door ajar ~1 inch)
  14. Read and record velocity in fpm
  15. Minimum acceptable: 200 fpm inward
  16. Repeat at glove port openings
  17. Record all readings

Phase 3: System Evaluation and Reporting (15 minutes)

  1. Compile all data: Ξ”P reading, tissue test results, smoke test results, velometer readings
  2. Compare to acceptance criteria:
  3. Ξ”P within manufacturer's range? β–‘ Yes β–‘ No
  4. All tissue tests show inward pull? β–‘ Yes β–‘ No
  5. All smoke tests show inward capture? β–‘ Yes β–‘ No
  6. Velometer readings β‰₯200 fpm? β–‘ Yes β–‘ No
  7. Write an assessment summary:
  8. Overall system status (Pass / Marginal / Fail)
  9. Any deficiencies identified
  10. Recommended corrective actions
  11. Present findings to instructor for review
  12. If any test failed: discuss what maintenance or repair is needed

Discussion Points

  • What does a high Ξ”P reading tell you about the system's condition?
  • Where did you find the weakest capture velocity? Why might that location be vulnerable?
  • How would duct leaks affect the system's performance at the cabinet?
  • What would happen if the dust collector was turned off but blasting continued?

Expected Outcomes

  • Students collect quantitative and qualitative ventilation performance data
  • Students correctly interpret Ξ”P readings relative to filter life
  • Students identify any containment failures using smoke visualization
  • Students produce a written assessment with actionable recommendations

Assessment Rubric

Criterion Excellent (4) Proficient (3) Developing (2) Beginning (1)
Data collection All measurements taken correctly Most measurements correct Some measurements missed Incomplete data
Smoke tube technique Smooth, controlled smoke release at all test points Good technique, minor issues Inconsistent technique Unable to generate usable smoke stream
Data interpretation Correct assessment with technical reasoning Correct assessment Partially correct Incorrect assessment
Report quality Complete, clear, actionable recommendations Good report with recommendations Basic report Incomplete report

Safety Considerations

  • Smoke tubes contain sulfuric acid β€” handle with care, do not break in enclosed spaces
  • Use the aspirator bulb for smoke generation β€” never inhale through the tube
  • Dispose of used smoke tubes in chemical waste, not regular trash
  • Wear safety glasses during testing
  • Do not operate the blast cabinet during ventilation testing β€” test the ventilation system without blasting

Last Updated: 2026-03-19