FE Environmental Practice Question Solution included after investigation
CASE E-076 Β· FE

The Two Collectors That Removed 94%, Not 150%

A 70% cyclone followed by an 80% baghouse did not provide 150% removal. The second device treated only what escaped the first, giving 94% overall removal.

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Inspect, commit, prove, fix, and sign off.

Case E-076 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field β€” in five guided steps.

1

Inspect

Review the problem, diagram, and evidence.

2

Commit

Choose your hypothesis.

3

Prove

Run calculations and test your idea.

4

Fix

Select and validate a safe correction.

5

Sign Off

See the full debrief and key takeaways.

Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A particulate stream of 100 kg/hr enters a cyclone with 70% collection efficiency, followed by a baghouse with 80% collection efficiency based on the particulate entering the baghouse. A note adds the efficiencies and reports 150% removal. Determine the outlet particulate rate and overall collection efficiency.

Air Quality Control Environmental Design Verification Root Cause Analysis Safe Correction
E-076
INVESTIGATION WORKSPACE WORK THROUGH THE CASE β€” YOUR CHOICES MATTER.
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DEBRIEF (LOCKED)

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Find the root cause, confirm the fix, and see how this connects to the exam.

πŸ”’Root causeComplete the case
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πŸ”’Correct fixComplete the case
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πŸ”’Exam takeawayComplete the case
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CASE CLOSED Β· ENGINEERING VERDICT

What actually failed β€” and what should change.

What failed

Two collection percentages were added directly.

What was missed

The baghouse receives only the particulate that escapes the cyclone.

Corrected model

Use Ξ·overall=1-(1-Ξ·1)(1-Ξ·2) for the stated two-stage series system.

QUICK ANSWER

The cyclone leaves 100(1-0.70)=30 kg/hr. The baghouse leaves 30(1-0.80)=6 kg/hr. Overall collection is 1-6/100=94%.

ENGINEERING TAKEAWAY

For independent series devices, the overall fraction remaining is the product of the stage fractions remaining: (1-Ξ·1)(1-Ξ·2).

CASE QUESTIONS

Questions this case should settle.

How do you combine two particulate collection efficiencies in series?

Use Ξ·overall=1-(1-Ξ·1)(1-Ξ·2).

What second-stage efficiency is needed for 98% overall removal after a 70% first stage?

About 93.3%.

NEXT FE PRACTICE QUESTION

The Room That Stabilized at 6.5 mg/mΒ³, Not 0.2

Air Quality Control Β· 5–10 min

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WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams β€” and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
COMMON QUESTIONS
Do I need prior knowledge to use these cases?

Basic subject familiarity helps, but every case is designed to teach through the investigation itself.

How long does a case take?

Most cases are designed for a focused 5–10 minute investigation.

Are the cases aligned with engineering exams?

Each case is mapped to a verified exam, subject, topic, and misconception before publication.

What happens after I complete a case?

The sealed debrief unlocks with the root cause, corrected reasoning, fix, and takeaway.