How to perform a risk assessment before non-routine maintenance

Non-routine maintenance refers to unplanned/special work: mill disassembly, classifier wheel removal, bag filter overhaul, pressure gauge/thermocouple replacement, pipeline blockage clearing, roller alignment, jet mill nozzle cleaning, etc.

Graphite dust is combustible, conductive, explosive, and toxic by inhalation, so risk assessment must target these hazards before any non-daily work.

Below is a field-operable 7-step risk assessment procedure with graphite-specific hazard identification and control measures.

0. Precondition: Define the Maintenance Scope First

Before assessment, confirm:

• Exact work content & location (mill interior? baghouse? duct? instrument panel?)
• Shutdown mode (full stop / partial stop)
• Tools needed (welding? grinding? explosion-proof vacuum? lifting?)
• Number of operators & duration
• Whether nitrogen purging, hot work, confined space entry is involved

Step 1: Identify All Hazards (Graphite Plant-Specific)

List every possible hazard for the non-routine task:

1.1 Dust & Explosion Hazards (Highest Risk)

• Graphite dust cloud formation during cleaning/dismantling
• Static electricity from friction, airflow, improper grounding
• Ignition sources: sparks from metal tools, hot surfaces, electrical arcs
• Dust accumulation re-entrainment leading to secondary explosion

1.2 Mechanical Hazards

• Accidental equipment startup (LOTO failure)
• Crushing/collision from heavy parts (roller, classifier wheel)
• Sharp edges cutting hands
• Material collapse (blocked graphite falling suddenly)

1.3 Gas & Suffocation Hazards

• Nitrogen purging in jet mill → oxygen deficiency
• Residual acid fumes (if purification section maintenance)
• Poor ventilation in confined spaces (mill, baghouse, duct)

1.4 Electrical Hazards

• Graphite dust is conductive → short circuit / electric shock
• Damaged explosion-proof instruments / cables
• Unauthorized live working

1.5 Physical Hazards

• High temperature surface burns (dryer, kiln, just-stopped mill)
• Condensation → slipping
• Climbing height (bag filter top, mill platform) → fall
• Dust inhalation → respiratory damage

1.6 Instrument & Control Hazards

• Wrong disconnection of thermocouple / pressure transmitter → false signal
• Pressure tube rupture → air blow + dust spray

Step 2: Risk Level Evaluation (Simplified LEC Method for Site Use)

Assess each hazard by Likelihood × Consequence and grade risk:

• Red (High risk): Must eliminate before work
• Orange (Medium risk): Strict control measures required
• Blue (Low risk): Routine protection

Red high-risk items that must be resolved first:

• Confined space without oxygen monitoring
• No LOTO lock
• Humidity <40% (static explosion risk)
• Ungrounded equipment
• No explosion-proof tools

Step 3: Develop Hierarchical Risk Control Measures

Follow the sequence: Eliminate → Isolate → Engineering → Administrative → PPE

A. Explosion & Static Control (Core for Graphite)

• Workshop humidity controlled at 40–55% RH
• All equipment reliably grounded (resistance ≤4Ω)
• Use only explosion-proof, non-sparking tools (brass, plastic scraper)
• Prohibit iron knocking, friction, grinding, hot work
• Dust cleaned by explosion-proof vacuum only; no compressed air blowing
• Maintain nitrogen purge if needed, keep O₂ <12% in grinding chamber

B. Mechanical Safety (LOTO Strictly Implemented)

• Cut off electricity, air pressure, hydraulic, nitrogen → lock & tag
• Confirm zero energy: no pressure, no rotation, no material movement
• Isolate feed inlet & discharge outlet to prevent material sliding

C. Confined Space / Suffocation Control

• Test oxygen concentration first: 19.5–23.5%
• Forced ventilation ≥30 min before entry
• Equip with portable O₂ alarm & walkie-talkie
• Set outside guardian; no solo operation

D. Dust & Respiratory Protection

• Wear P100/N95+ respirator, anti-static coveralls, conductive gloves
• Negative pressure in operation area; dust collection running
• Minimize dust disturbance; clean gradually

E. High Temperature & Electrical Safety

• Cool equipment to <40°C before touching
• No live disassembly of instruments; cover electrical connectors
• Anti-slip treatment for condensation areas

F. Instrument Maintenance Special Control

• Mark wiring before disconnecting thermocouple / pressure sensor
• Plug pressure tapping port to avoid dust entry
• Calibrate after replacement to avoid false readings

Step 4: Fill in the Job Safety Analysis (JSA) Form

A one-page form for workshop use, must include:

1. Work item & location
2. Personnel & supervisor
3. Identified hazards
4. Risk level
5. Control measures
6. Emergency measures
7. Signature of assessor & approver

Must not start work without signed JSA.

Step 5: On-Site Toolbox Meeting (5–10 Min)

Before starting maintenance, the supervisor must confirm:

• All control measures in place
• Everyone knows hazards & emergency steps
• LOTO, grounding, ventilation, PPE are ready
• Emergency equipment nearby: fire extinguisher, first-aid kit, oxygen detector

Step 6: Real-Time Risk Monitoring During Operation

• Check humidity, static, oxygen concentration at intervals
• Stop work immediately if:
  • Dust cloud forms
  • Static sparking
  • Abnormal odor / oxygen alarm
  • Loose LOTO lock
• No temporary modification of control measures

Step 7: Post-Maintenance Risk Closeout & Review

After work finished:

• Clean residual graphite dust completely
• Restore safety devices (grounding, filters, alarms)
• Test instruments & equipment function
• Record risks encountered & improvements
• Archive JSA form for future similar work

Typical High-Risk Non-Routine Tasks & Key Checks

Emergency Response Reserved in Assessment

• Dust fire: Use dry powder extinguisher; no water
• Explosion risk: Evacuate immediately, activate alarm
• Suffocation: Move to fresh air, call first aid
• Electric shock: Cut power first, rescue
• Dust inhalation: Fresh air, medical treatment

Core Golden Rules for Graphite Plant

1. No risk assessment → No maintenance work
2. No LOTO → No entry into equipment
3. Humidity out of range → No dust cleaning
4. Non-explosion-proof tools → No operation
5. No guardian → No confined space work