Thermite / Aluminothermic Welding SWMS

Thermite (aluminothermic) welding uses an exothermic reaction between aluminium powder and metal oxide to produce molten steel exceeding 2,500°C, used for rail joint welding, cathodic protection bonding, and earthing connections (Cad-weld). The reaction is violent, fast, and irreversible once ignited, generating molten metal ejection, intense radiant heat, metal fume, and ignition sources for surrounding combustibles. Under WHS Regulation 2011 r291, hot work involving risk of fire or explosion is classified as High Risk Construction Work, mandating a Safe Work Method Statement before work commences. The SWMS must address crucible preparation, mould alignment, ignition procedures, exclusion zones, fume capture, and emergency response for runaway reactions or mould failure. PCBUs failing to prepare, communicate, and enforce this SWMS expose workers to severe burns, respiratory injury, and ignition of surrounding assets including rail corridor vegetation or live substation equipment.

Hazards identified

7 hazards covered, sorted by priority.

Control measures

Hierarchy-of-controls order: elimination → substitution → isolation → engineering → administrative → PPE.

1. 1Elimination — Where feasible, specify exothermic cable connectors or mechanical compression joints in design to eliminate molten metal process entirely from earthing scopes.
2. 2Elimination — Schedule thermite work outside Total Fire Ban days and high wind periods to eliminate uncontrolled ignition pathways in rail and bushland corridors.
3. 3Substitution — Substitute traditional magnesium starter powder with electronic spark igniters where manufacturer permits, reducing premature ignition and flare-up risk to the operator.
4. 4Substitution — Use single-shot pre-packaged cartridges in sealed moisture-proof sachets rather than bulk powder decanting to substitute lower-risk handling format.
5. 5Engineering — Pre-heat graphite moulds with oxy-LPG torch to 150°C minimum to drive off moisture before charging, eliminating steam explosion mechanism per manufacturer IFU.
6. 6Engineering — Establish 6-metre combustible-free exclusion zone with fire blankets, wet-down of vegetation, and dedicated 9kg dry powder extinguisher plus charged hose within arm's reach.
7. 7Administrative — Issue rail authority Track Possession or Electrical Access Permit and isolate traction return before welding to bonded conductors; verify dead with approved tester.
8. 8Administrative — Pre-start brief crew on this SWMS, confirm crucible condition, mould part-number match, and nominate spotter for fire watch 60 minutes post-tap.
9. 9PPE — Aluminised reaction jacket and leggings to AS/NZS 4501.2, leather gauntlets, shade 5 goggles under face shield, and P2 respirator with metal fume cartridge.
10. 10PPE — Steel-cap boots with metatarsal guard and natural-fibre underlayer; no synthetics that melt onto skin during molten metal splash event.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

On a regional rail upgrade, a two-person welding crew is scheduled to install eight Cad-weld bonds connecting impedance bond cables to running rail during a four-hour Sunday possession. At the pre-start brief in the rail compound, the leading hand opens this SWMS on a tablet and walks the offsider through each hazard line by line. They identify that the day's forecast is 32°C with gusty westerly winds — the SWMS exclusion-zone control prompts them to wet down ballast and surrounding grass for six metres around each weld location and to confirm the Total Fire Ban status with the rail protection officer. The offsider sights the aluminised jackets, shade 5 goggles, and P2 fume respirators against the PPE checklist and signs on. During the third weld, the leading hand notices the graphite mould has a hairline crack from the previous shot; the SWMS mould-integrity control requires immediate rejection, so they swap to a spare mould before charging. After tap, the offsider commences the 60-minute fire watch documented on the back of the SWMS, with the dry powder extinguisher staged within arm's reach. The signed SWMS is returned to the site office and retained on the project HSE register.

Related legislation

• WHS Act 2011 (model)
• WHS Regulation 2025
• Code of Practice — Hazardous Manual Tasks

Frequently asked questions