2026 12개년 산업안전산업기사 필기 4과목 1~50번 몰아보기

Main Ideas & Concepts Covered

The video is an exam-prep walkthrough (likely for Korean Industrial Safety Engineer / “산업안전산업기사” 필기) focusing on multiple-choice questions from the industrial safety / fire–explosion prevention area. The speaker repeatedly:

• States a concept
• Compares answer choices
• Selects the correct numbered option
• Explains key distinctions (especially classifications, symbols, and safety structures)

Electrical hazard classifications for voltage

• Correctly distinguishing low voltage, high voltage, and extra-high voltage across DC vs AC thresholds.
• Identifying which option is incorrect regarding voltage classification.

Explosion hazard classification & “flame trajectory limit” (화염비행거리 한계)

• Relating an explosion/gas grade to the risk of flame propagation.
• Emphasizing that grade numbering can feel non-intuitive (e.g., “Grade 3 is bigger than Grade 1” in the given context).
• Using the gap concept:
  • Smaller flame trajectory limit → greater external ignition risk
  • Hence, the importance of “gap” in prevention logic.

Explosion-proof structure types, symbols, and incorrect pairings

• Dustproof explosion-proof structures:
  • identifying which one corresponds to dustproof/explosion-proof designations.
• Recognizing which structures are not explosion-proof types.
• Matching structure names ↔ notation symbols, such as:
  • pressure-resistant
  • intrinsically safe
  • non-ignition / non-sparking concepts
  • safety verification methods
• Multiple questions focus on correct symbol-letter mapping and avoiding mismatches.

Hazardous locations classification (gas/vapor vs dust)

Gas hazardous areas (Class 0/1/2)

• Class 0: long-term/continuous presence (described as “long-term” occurrence)
• Class 1: periodic/frequent presence
• Class 2: rarely or only abnormal/short duration
  • “abnormal state” is contrasted with normal conditions

Dust hazardous areas (Type 20/21/22)

• Type 20: continuous or frequently present dust cloud
• Type 21: likely intermittent or frequently present during normal operation

• Type 22: abnormal condition, rarely, short duration

• Selecting which description does not belong to gas or dust categories and matching types to definitions.

Explosion-proof equipment selection: “least relevant” consideration

• When choosing certified explosion-proof equipment, multiple technical factors are mentioned.
• The video teaches that among the choices, one is the “least relevant” based on which property aligns with the required structure/type.

Testing & performance testing (pressure-resistant explosion-proof electrical machinery)

• Explains how performance testing is conducted, including:
  • installed contents vs. samples from testing/impact tests
  • and testing conditions when parts are not required to be enclosed
• Emphasizes testing under extreme/harsh conditions.

Specific explosion-proof design methods

Includes common approach categories and reasoning:

• Pressure-resistant: withstands internal explosion and prevents “splashing out”
• Inert gas purging/pressurization: prevents explosive atmosphere from entering
• Increased safety: additional measures to prevent excessive temperature rise/arcing/sparking
• Encapsulation / potting / compound filling (mold/compound):
  • prevents ignition by covering
• Repeated “choose the structure type” logic appears throughout the examples.

Maximum safe gap / standard

• Safe gap limits are explained as relating to explosion class standards (mentions IEC and another standard resembling KGC).
• Identifies which option matches the correct maximum safe gap rule/range.

Protective equipment & safety devices in hazardous work

Shifts from explosion prevention into broader occupational safety and electrical work, including:

• Protective gear for high-risk charged furnace work (flame-retardant workwear)
• Correct matching of protective equipment to working conditions
• Arc welding: devices/gloves/insulating items vs what is not used
• AC welding machine: automatic rating protection device—what it does vs what it does not prevent (static electricity mentioned as “not” prevented)
• Live-line work: difference between protective gear vs protective devices
• High-pressure container safety:
  • safety valve/relief devices (melting part to create gas vent)
  • rupture disk / safety valve installation requirements
• Fire/explosion prevention accessories:
  • flame arrestor components for welding
  • flame arrester “anti-flashback” structure composition
  • flame arrestor devices (e.g., flame mesh/guard/net concepts)

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Methodology / Instruction-Style Content

How to classify voltage (to pick the “incorrect” option)

1. Determine whether the supply is DC or AC.
2. Apply threshold rules as described:
   • Low voltage (DC): “1.5 kV or less”
   • Low voltage (AC): “1 kV or less”
   • High voltage (DC/AC range): “1.5 kV or more and up to 7 kV”
   • High voltage (AC): “over 1 kV and up to 7 kV”
   • Extra-high voltage: exceeding 7 kV (treated as special/extra-high)
3. If an option claims a mismatched category (example given: “low-voltage DC 1.5 kV” treated as “high-voltage AC 1–7 kV”), treat it as incorrect.

How to judge explosion grade vs flame trajectory limits

• Use flame trajectory limit logic:
  • Smaller flame trajectory limit → greater external ignition risk
• Decide correctness by matching statements to the “gap” concept:
  • “Set the gap small” is used to align with the correct reasoning.

How to select the correct explosion-proof structure symbol/type

• Read the question: is it asking for a dustproof structure, intrinsically safe structure, safety verification method, pressure method, safety-enhanced structure, etc.?
• Match:
  • Structure name ↔ correct symbol/letter notation
• Mark incorrect any option that swaps mismatched pairings (examples mentioned):
  • “pressure” vs “inflow prevention”
  • “intrinsic safety method” vs “safety verification method”
  • wrong mapping of the numeric option

How performance testing is performed for pressure-resistant explosion-proof equipment

• If asked “incorrect statement”:
  • The taught correct pattern includes:
    • performance testing is not necessarily done with all content installed
    • tests may use samples that underwent impact tests
    • if parts can be used without being enclosed, testing must still be done under most extreme/harsh conditions

How to approach hazardous location (gas/dust) classification questions

Gas hazardous locations

• Identify the time/frequency category:
  • continuous/long-term
  • periodic/frequent
  • rarely or abnormal/short duration
• Map to Class 0 / 1 / 2 as described.

Dust hazardous locations

• Map based on:

  • continuous/frequent during normal operation (Type 20)
  • likely intermittently present/frequent during normal operation (Type 21)
  • abnormal/rare/short duration (Type 22)

• Choose the option that either doesn’t belong or correctly matches the described scenario to the type.

How to interpret “least relevant” vs “most relevant” in equipment selection

• Identify which parameter is tied to the structure type (examples mentioned):
  • pressure method: highest surface temperature & max safety gap relevance
  • safety increase method: max surface temperature relevance vs max safety gap (treated as not relevant)
  • intrinsic safety: minimum ignition current relevance
• Select the option that refers to a parameter not applicable to the structure type being tested.

How to reason about wearables vs installed safety devices (live-line work)

• Distinguish:
  • Protective gear: workers wear (e.g., insulating gloves/suits)
  • Protective devices: installed equipment (e.g., insulating protection devices)
• If an option incorrectly treats “gear” as a device (or vice versa), mark it incorrect.

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Correct / Selected Answer Numbers (as stated by the speaker)

Note: These are the speaker’s claims based on the subtitles/Q&A (multiple questions across the video).

• Voltage classification incorrect: #4
• Flame trajectory limits & explosion grades incorrect: #3
• Dustproof explosion-proof structure symbol: #2
• Explosion-proof structure type “not a type” question: #1
• Inflow/explosion-proof room structure symbol mismatch: #4
• Explosion-proof structure name/notation mismatch: #3
• Correct type/symbol matching: #1
• Explosion-proof electrical equipment symbol for gas explosion classes 1&2 (G1–G4): #1
• Correct range for “bal(a) point” of “Barado G1” (as phrased): #1
• Explosion classification hazardous locations gas-types “does not belong”: #4
• Hazardous location corresponding to description (“risk of dangerous concentrations”): #2
• Class 1 hazardous area correspondence in explosion-proof facilities: #2
• Name for Class 1 location among classifications: #3
• Type/place corresponding to explosion risk (periodic/frequent): #2
• Methods/structures not usable in Class 1 gas explosion areas: #4
• Not total enclosed type question: #4
• Method definition about preventing gas entry by inert gas injection (pressure purging): #2
• “Performance testing… incorrect statement” question: #3
• Intrinsic/increased safety structure definition: #3
• Safety-enhanced explosion-proof structure description: #3
• Compound filling/mold method description: #1
• Least necessary measure to prevent hazardous atmosphere due to regular equipment: #1
• Maximum safe gap standard question: #4
• “Basics of explosion protection not suitable as general method”: #4
• Least relevant consideration when selecting explosion-proof equipment: #3
• “Minimum ignition current” (intrinsically safe method structure): speaker associates with #4, then “correct answer is #3” appears (subtitles conflict)
• Certified equipment indication requirements question (furthest from requirements): #2
• Dust explosion hazard locations “does not fall under”: #4
• Dust hazardous location type for continuous/long-term flammable dust: #3
• Classification description applies to hazardous locations: #1
• Protective seals handling hazardous materials—statement about no appearance requirement: #4
• Not a safe task for handling hazardous substances: #3
• Explosion-proof tools commonly used materials question: #4
• Required workwear for charged furnace arc/spark burn risk: #2
• Protective equipment connection not suitable: #2
• Protective gear for falling objects/impact/entrapment/electric shock/electrostatic: #3
• Arc welding: “not used to prevent electric shock”: #1
• AC welding machine accident prevention device: #1
• Incorrect statement about automatic rating protection device function in AC welding: #3
• Not protective equipment required for high-voltage live-line work: #1
• Not safety equipment used during live-line work: #4
• Safety device in high-pressure containers that melts metal to vent: #1
• Pressure relief device installed in pressure vessels question: #3
• NOT an advantage of an open-type spring safety valve: #3
• Advantage check for leaks between valve seat and stem: #3
• “Device designed to prevent flame spread” (flame arrester/net concepts): #1
• Flashback arrestor structure description incorrect: #1
• Most suitable method for safe use of insulating rubber gloves: #4
• Wearing order for rubber gloves example: #4

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Speakers / Sources Featured

• Dobi (video presenter/instructor; repeatedly addressed as “Hello everyone. This is Dobi.”)
• Auto-generated subtitles source (no named external organizations beyond mentions of standards like IEC and “KGC,” referenced as standards rather than separate speakers)