CHST Exam – Inclusive Numeric Thresholds & Calculations Guide

1️⃣ Excavations & Soil Classification (OSHA Subpart P)

• Type A Soil: ≥ 1.5 tsf (144 kPa) → Slope ¾:1 (53°)

• Type B Soil: 0.5–1.5 tsf (48–144 kPa) → Slope 1:1 (45°)

• Type C Soil: ≤ 0.5 tsf (48 kPa) → Slope 1½:1 (34°)

• Deeper than 20 ft → must be designed by a Registered Professional Engineer.
  👉 Exam Trap: even if soil = Type A, if depth >20 ft, answer is “PE design.”

2️⃣ Noise Exposure (OSHA vs. NIOSH)

• OSHA PEL: 90 dBA (8 hr TWA) with 5 dB exchange rate.

• Action Level: 85 dBA (8 hr TWA).

• NIOSH REL: 85 dBA (8 hr TWA) with 3 dB exchange rate.

• Doubling Rule: Every +3 dB (NIOSH) or +5 dB (OSHA) = half the allowable time.
  👉 Example: OSHA allows 2 hours at 100 dBA, but NIOSH only 15 minutes.

• NIOSH Method 7500 (Silica Dust): Flow rate 2.5 L/min with cyclone.

3️⃣ Confined Space Atmosphere

• Oxygen range: 19.5% – 23.5%.

• Testing order: O₂ → flammables (LEL) → toxics.

• LEL (Lower Explosive Limit): Evacuate if ≥ 10% LEL.

• IDLH: Immediately Dangerous to Life or Health → requires supplied-air or SCBA.
  👉 Exam Trap: They often ask “what gas first?” → Always oxygen first.

4️⃣ Fire Extinguishers (NFPA 10)

• Class A: Ordinary combustibles (wood, paper).

• Class B: Flammable liquids (gasoline, oil).

• Class C: Electrical fires.

• Class D: Combustible metals (magnesium, sodium).

• Class K: Kitchen oils/fats.

• Type ABC: Multipurpose dry chemical.
  👉 Rule of thumb: If scenario has multiple hazards (combustibles + liquids + electrical) → Answer = Type ABC.

5️⃣ PPE Standards (ANSI / OSHA)

• Hard hats (ANSI Z89.1)

  • Class G: General, up to 2,200 V.

  • Class E: Electrical, up to 20,000 V.

  • Class C: Conductive, no electrical protection.

• Eye/Face (ANSI Z87.1) → Impact, splash, UV.

• Fall Protection (OSHA 1926.501)

  • Trigger heights: 6 ft (construction), 4 ft (general industry).

  • Scaffold: 10 ft.

  • Excavations: 6 ft deep requires protection.

6️⃣ Respiratory Protection (OSHA 1910.134)

• Air-purifying (APR): N95, P100, etc.

• Powered APR (PAPR): Battery powered, less strain.

• Supplied-air (SAR): Airline respirators.

• SCBA: Self-contained, IDLH.

• CE blasting hood: Required for abrasive blasting with lead.
  👉 Trap: If IDLH or unknown concentration → Always SCBA/SAR.

7️⃣ Heat & Cold Stress

• Heat stroke: Hot, dry skin, no sweating → Medical emergency, call 911.

• Engineering control for heat: Shading, ventilation, hydration.

• Cold stress control: Provide warming shelters.

• Work/rest cycles: Apply when temps >85°F + PPE.

8️⃣ Silicosis Latency

• Chronic silicosis: ≥ 10 years.

• Accelerated silicosis: 2–5 years (prep key answer).

• Acute silicosis: Weeks to <2 years.
  👉 Exam Trap: Even though OSHA/NIOSH say 5–10 yrs for accelerated, Yates prep key = 2–5 yrs.

9️⃣ Radiation Protection

• Most effective shielding: Lead > concrete > water.

• Inverse square law: Double the distance = ¼ exposure.

🔟 Emergency Planning (EAP / ICS)

• EAP Minimum Requirements (OSHA 1910.38):

  1. Procedures to report emergencies.

  2. Evacuation routes & procedures.

  3. Procedures to account for all employees after evacuation.

  4. Shutdown of critical operations.

• ICS Key Roles: Incident Commander, Safety Officer, Liaison, Public Information Officer, Section Chiefs.
  👉 Exam Trap: If question says “what is minimum requirement?” → Answer = accounting for employees.

1️⃣1️⃣ Ergonomics & Hand-Arm Vibration

• Neutral posture: Avoid bent wrists, elbows at ~90°.

• Natural range of motion: Required.

• HAVS (Hand-Arm Vibration Syndrome): Vibration-induced white finger worsened by cold conditions.

1️⃣2️⃣ General Safety Numbers

• Ladder safe angle: 4:1 (1 ft out for every 4 ft up).

• Portable gasoline cabinet sill: 2-inch liquid-tight pan.

• Hard hat impact test (ANSI Z89.1): 3.6 kg weight, max 4,450 N force transfer.

• Fall arrest descent rate: 2–4 ft/sec for self-rescue systems.