Ammonia (NH3) Industrial Refrigeration SWMS

Industrial ammonia (NH3/R717) refrigeration plant maintenance covers some of the highest-consequence work in Australian food processing, cold storage and abattoir facilities. Tasks include charge top-up and decanting, compressor and valve isolation, oil drain, leak-detection audits, purger servicing and emergency response drills involving SCBA. Anhydrous ammonia is classified as a Schedule 11 hazardous chemical under the Model WHS Regulations and is acutely toxic by inhalation (IDLH 300 ppm), flammable between 15–28% v/v in air, and corrosive to respiratory tissue and eyes. Under WHS Regulation Part 7.1 and AS/NZS 5149.3, any work that may release ammonia, enter a machinery room classified as a hazardous area, or break containment on a charged system is High Risk Construction Work requiring a documented SWMS before the task commences. PCBUs operating manifold quantities above the placarding threshold (500 kg) also have notification and Major Hazard Facility duties. This SWMS provides the structured risk assessment, isolation sequence, hierarchy controls and emergency arrangements that the regulator and your insurer expect.

Hazards identified

7 hazards covered, sorted by priority.

Control measures

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

1. 1Elimination — Where feasible, pump down and remove ammonia charge from the work section to the high-pressure receiver before any containment break, verified by gauge and temperature.
2. 2Elimination — Schedule major valve and pipework intervention during planned plant shutdown so live decanting and hot work on charged lines is avoided entirely.
3. 3Substitution — Replace obsolete packed gland valves with diaphragm or bellows-sealed isolation valves to AS/NZS 5149.2 to remove the chronic micro-leak source.
4. 4Engineering — Maintain fixed electrochemical NH3 detection at 25 ppm alarm and 150 ppm trip, interlocked to mechanical ventilation delivering 30 air changes per hour per AS/NZS 5149.3 clause 9.
5. 5Engineering — Install double-block-and-bleed isolation with locked bleed to a scrubber or water-curtain dump tank before any flange break on liquid lines above 100 mm.
6. 6Engineering — Provide hazardous-area-rated emergency stop, deluge water curtain at engine-room doors and remote king valve closure from a safe muster point.
7. 7Administrative — Issue permit-to-work, lockout-tagout and confined space entry permit for plant room work, with chief refrigeration engineer countersigning isolation boundary diagrams.
8. 8Administrative — Conduct pre-start brief against this SWMS, verify SCBA cylinder pressure above 250 bar, confirm standby attendant, retrieval line and two-way radio comms before entry.
9. 9PPE — Issue ammonia-rated chemical suit (butyl or Viton) to EN 943, full-face SCBA with 30-minute cylinder minimum, cryogenic gauntlets and splash-proof eye protection for all decant tasks.
10. 10PPE — Position escape respirators (15-minute ammonia-rated hood) at every plant room exit and at the compressor deck for non-entry workers to self-evacuate above 25 ppm alarm.

Applicable Codes of Practice

High-Risk Construction Work triggered

Worked example

At a regional poultry processing facility, a refrigeration crew is scheduled to replace a leaking liquid solenoid valve on a −38°C blast freezer suction main holding approximately 80 kg of liquid ammonia. At the 6:30 am pre-start, the lead technician opens this SWMS on a tablet and walks the two-person crew and the plant operator through it. Hazard 1 (inhalation) and Hazard 5 (hydraulic shock) are flagged as the critical concerns for today's task. The crew confirms the engineering controls: the section has been pumped down to the high-pressure receiver overnight, the king valve is locked closed, double-block-and-bleed isolation is rigged to a water dump drum, and the fixed NH3 detector reads 0 ppm with ventilation running at 30 ACH. Administrative controls are signed off — permit-to-work, LOTO tags applied to the screw compressor starter at the MCC, and the standby attendant is positioned outside the plant room with radio and escape respirator. PPE is verified: both technicians don butyl suits, cryogenic gauntlets and SCBA with cylinders showing 280 bar. Each worker physically signs the SWMS sign-on register. Mid-task, the bleed valve releases a brief vapour puff and the portable detector alarms at 35 ppm; per the document's trigger response, the crew withdraws, increases ventilation, and re-enters only when readings fall below 10 ppm, logging the deviation on the SWMS review section.

Related legislation

• WHS Act 2011 (model)
• WHS Regulation 2025
• AS 2865 — Confined spaces

Frequently asked questions