FE Other Disciplines Practice Question Solution included after investigation
CASE E-091 · FE

The Confined Space That Needed 18 m³/min, Not 1,080

Six air changes per hour sounded like 1,080 m³/min when the hour-to-minute conversion was skipped. The required flow was 18 m³/min.

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

Case E-091 engineering failure visual
HOW THIS WORKS

Think like
a real engineer.

Follow the investigation process used in the field — 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 confined space has a volume of 180 m³. A ventilation plan specifies 6 air changes per hour. A note multiplies 180×6=1080 and reports 1080 m³/min. Determine the correct required ventilation flow in m³/min and the corresponding nominal air-replacement time.

Safety Health Environment Other Disciplines Design Verification Root Cause Analysis Safe Correction
E-091
INVESTIGATION WORKSPACE WORK THROUGH THE CASE — YOUR CHOICES MATTER.
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

An hourly volumetric rate was mislabeled as a per-minute rate.

What was missed

The 60 min/hour conversion.

Corrected model

Use Q=V×ACH/60 when Q is required in m³/min.

QUICK ANSWER

For a 180 m³ space at 6 ACH, Q=180×6=1080 m³/h=18 m³/min. One nominal air change therefore takes 10 minutes.

ENGINEERING TAKEAWAY

For ACH in h^-1, Q=V×ACH gives volume per hour. Divide by 60 to express the result in m³/min.

CASE QUESTIONS

Questions this case should settle.

How do you convert ACH to ventilation flow?

Use Q=V×ACH, then convert the resulting time unit as needed.

What is the nominal air-change time at 6 ACH?

10 minutes per air change.

NEXT FE PRACTICE QUESTION

The Relief Valve That Saw 480 N, Not 560

Safety Health Environment · 5–10 min

Continue Practice →
WHAT YOU’LL LEARN

Real failures. Lasting skills.

Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — 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.