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Safety Protocol 001: CNC Plasma Table Operation Safety

Protocol ID: U5M3-SAFE-001 Context: Safety procedures specific to CNC plasma table operation, including electrical lockout, THC hazards, water table management, and multi-person shop protocols Hazard Level: Very High — Combines electrical (300V OCV), thermal (30,000°F+), radiation, fume, and noise hazards simultaneously

Potential Hazards

CNC-Specific Electrical Hazards

  • Open circuit voltage: 200-300V DC present at the torch whenever the power supply is armed — lethal voltage. The torch can energize without visible arc during pilot arc initiation
  • Water table + electricity: Water conducts electricity. Contact with water while the torch is energized creates shock risk. Water table grounding must be verified
  • THC probing: During IHS (Initial Height Sense), the torch descends and makes contact with the workpiece — the touch-sense circuit energizes the torch tip

CNC-Specific Mechanical Hazards

  • Gantry movement: The gantry moves at rapid traverse speeds (up to 500 IPM) and can crush fingers, hands, or tools left on the table
  • Automatic torch descent: The torch moves down automatically during IHS and pierce sequences — clearance hazards near the torch mount
  • Unexpected motion: After E-stop recovery, the machine may attempt to return to a programmed position — verify clear path before resuming

Water Table Hazards

  • Steam eruption: When the torch pierces directly over the water surface, steam can erupt violently, deflecting molten metal and potentially extinguishing the pilot arc
  • Hydrogen generation: Prolonged cutting over water can generate hydrogen gas (from water electrolysis). In enclosed spaces, hydrogen accumulation creates explosion risk — maintain ventilation
  • Electrical ground through water: If the water table is not properly grounded, the entire water volume can become energized

Required Precautions & Procedures

Before Operation

  1. Verify the plasma power supply main disconnect is OFF before any work on the torch, consumables, or table
  2. Test the E-stop function — press E-stop, verify all motion stops and arc cannot be initiated
  3. Verify the water table is properly grounded (ground rod or bonded to building ground)
  4. Ensure no personnel are working under, inside, or near the table before powering on
  5. Remove all tools, clamps, and loose items from the table surface and gantry path
  6. Verify welding screens are deployed around the cutting area — all personnel within 25 feet must be behind screens or wearing welding helmets

During Operation

  1. NEVER reach into the cutting area while the machine is running — the gantry can move without warning
  2. NEVER touch the torch, workpiece, or water while the power supply is armed — even without a visible arc, lethal voltage may be present
  3. Operator must remain at the controls (within arm's reach of E-stop and feed hold) for the entire duration of the cut
  4. If the machine pauses unexpectedly, do NOT approach — use the controller display to diagnose before clearing the alarm
  5. Monitor water table for excessive steam or boiling — indicates water level may be too high or material is positioned in the water
  6. Keep the shop doors/ventilation open — enclosed cutting produces ozone, NOx, and potentially hydrogen

Emergency Stop & Recovery

  1. Press E-stop to halt all motion and extinguish the arc
  2. After E-stop: the machine position may be lost. Note the line number in the G-code before approaching
  3. Before resuming: verify clear path for gantry travel, verify the torch is not touching the workpiece, verify consumables are intact
  4. Most controllers support "resume from line" — use this instead of re-running the entire program to avoid re-piercing completed features

Lockout/Tagout for Maintenance

  1. Turn off the plasma power supply at the main disconnect
  2. Turn off the CNC controller power
  3. Lock the main disconnect with a personal lock
  4. Apply a tag with your name and date
  5. Verify lockout by attempting to start the machine
  6. Only the person who applied the lock may remove it

Emergency Response

  1. Electrical shock from plasma system: Do NOT touch the victim. Disconnect power at the main disconnect using a non-conductive tool. Call 911. Begin CPR if victim is not breathing after being separated from the circuit
  2. Gantry collision with person: Press E-stop. Do not attempt to reverse the machine — call for assistance. Administer first aid for crush injuries
  3. Steam explosion/spatter: Press E-stop. Assess for burns — cool with running water 20 minutes. Seek medical attention for burns covering any significant area
  4. Water table fire: Press E-stop. If the fire is on the water surface (floating oil/debris), cover with fire blanket or use CO₂ extinguisher. Do NOT use water-based extinguisher on an electrical fire
  5. Arc flash to unprotected person: Move them away from the arc. Irrigate eyes with clean water for 15 minutes at eyewash station. Seek immediate medical attention. Symptoms may worsen over 6-12 hours

PPE Requirements

PPE Item Specification Required When
Welding helmet Shade 8-9 (<40A), Shade 9-12 (40A+), auto-darkening recommended All cutting operations
Safety glasses ANSI Z87.1, worn UNDER welding helmet Always in plasma area
FR jacket/shirt ASTM F1506 rated, long sleeve, snapped/buttoned All cutting operations
Leather gloves 14" gauntlet, no synthetic lining All cutting and material handling
Leather boots Steel/composite toe, 8"+ shaft Always in cutting area
Hearing protection NRR 25+ earmuffs or plugs All cutting operations
Respirator P100 half-face minimum (see U5M2-SAFE-001 for material-specific) All cutting operations
No synthetic clothing Polyester, nylon, rayon MELT into skin Never near plasma operations

Last Updated: 2026-03-19