Safety and Emergencies
Every refrigerant is a hazard, but the hazard is different for each one — know the fluid before you open anything.
Key Principles at a Glance 8 points
- The hazard depends entirely on the refrigerant — know which fluid is in the circuit before you open anything.
- R12 and R22 are non-toxic in normal concentrations but cause asphyxiation by oxygen deficiency in high concentrations, cause frostbite as liquid, and decompose in contact with flame to chlorine and phosgene.
- Refrigerant is heavier than air and collects in bilges, cold room floors and machinery space bottoms — treat a leak as an enclosed-space entry hazard.
- Ammonia is explosive between 16 and 25 % in air, poisonous and an irritant, and it attacks copper, so ammonia systems use ferrous materials only. Its high solubility in water means a wet cloth to the face gives some protection in an emergency.
- Two relief valves are required on a vessel greater than 285 litres, and no shut-off valve is permitted between the relief valve and the vessel it protects unless two such valves are fitted.
- A ruptured bursting disc is indicated by suction and discharge pressures being about equal — stop the machine, renew the disc, and investigate why it ruptured.
- The condition of the compressor oil is a direct indication of the physical and chemical cleanliness of the system; if it turns white and emulsified it is wet and must be drained and discarded.
- Remember TEWI — the energy-consumption term usually dominates the global warming impact, so keeping the condenser clean and the condensing pressure low is an environmental measure, not just an economic one.
1. What the Engineer Must Understand
The maker's manual, the SMS, the class rules and the M Notices override. No refrigerant is allowed to be released to atmosphere. All work on the refrigerant circuit is permit-controlled and requires the "man at work" board.
Every refrigerant is a hazard, but the hazard is different for each one. Know which fluid is in the circuit before you open anything.
| Refrigerant | Primary hazard | Secondary hazard |
|---|---|---|
| R12 (Freon 12) | Asphyxiation in high concentrations (oxygen deficiency) | Decomposes in contact with flame to chlorine and phosgene — pungent and poisonous. Gas escaping under pressure causes skin damage on contact |
| R22 | Similar to R12 | Not miscible with oil over the full temperature range |
| CO₂ | A leak can displace air and asphyxiate | Very high working pressures (70 bar discharge) — substantial construction required. Bottle pressure rises with temperature, relieved by a safety disc |
| R717 ammonia | Explosive between 16 and 25 % in air; poisonous; an irritant | Corrosive to copper and its alloys — ferrous materials only |
| Hydrocarbons (R290, R600a, R1270) | Highly flammable | Low GWP and ODP |
| All | Liquid refrigerant causes frostbite | Oil from a burnt hermetic motor contains halogen acids |
2. Asphyxiation
R12 is considered to be non-toxic except in high concentrations producing oxygen deficiency.
CO₂ is not explosive or flammable, but a leak is potentially dangerous because it can displace air and asphyxiate.
Refrigerant is heavier than air and will collect in bilges, cold room floors, machinery space bottoms and any low enclosed space. Never enter a space where refrigerant has leaked without:
- ventilating the space first,
- testing the atmosphere,
- a second man standing by at the entrance,
- breathing apparatus available.
This is a classic enclosed-space entry hazard and must be treated with the same discipline as any other enclosed space on board.
3. Decomposition in Flame — The Freon Hazard
Refrigerant 12 decomposes in contact with flame to give products which are pungent and poisonous — chlorine (Cl₂) and phosgene (COCl₂).
The practical consequences:
- Staff should be forbidden to smoke while leak testing or repairing. Many operatives are ignorant of the danger to their health if smoking in the presence of traces of the halocarbons.
- Never use a naked flame to search for a leak on a halocarbon system other than a purpose-made detector lamp, and never in an unventilated space.
- In a fire involving a halocarbon plant, the decomposition products are far more dangerous than the refrigerant itself. Breathing apparatus is mandatory.
- An open compressor's mechanical seal must never be "checked" with a flame.
4. Frostbite and Cold Burns
Liquid refrigerant at evaporator temperature will cause severe cold burns on contact with skin, and permanent eye damage.
Precautions:
- Wear gloves and goggles when handling charging lines, opening valve caps, and working on any line which may contain liquid refrigerant.
- Never point a charging line or a purge valve at yourself or another person.
- Keep the charging cylinder upright to prevent entry of liquid when the connection is made to the suction side of the system.
- Do not touch frosted pipework or evaporator surfaces with bare hands.
5. Ammonia — The Special Case
Thermodynamically, ammonia is a good refrigerant, but it is explosive, poisonous and an irritant. The explosive mixture is 16 to 25 per cent in air. It is corrosive to copper and its alloys, so that ferrous materials are used for components in a system employing ammonia.
Ammonia is highly soluble in water, with which it forms ammonium hydroxide, a weak base. About 1300 volumes of ammonia can be dissolved in 1 volume of water at low temperature, however it is easily expelled by boiling. The high solubility in water also means that a wet cloth held to the face will give some protection against an ammonia leak in an emergency, although a breathing apparatus would be worn in such a case, normally.
Because of the hazards, ammonia is used mainly ashore and on fishing vessels.
Operational consequences:
- Continuous oil migration — attention every week or, in some cases, every day.
- Oil drainage pots and low-point drains on condensers, receivers and evaporators; removal is a periodic manual function.
- Water-cooled cylinder heads are required because of the high discharge temperature.
- All jointing of lead or soft iron, and steel tubing, because non-ferrous metals are attacked.
- Leaks of R.717 usually make themselves apparent and motivate staff to search out the leak and repair it.
Emergency response to an ammonia leak:
6. High Pressure and Mechanical Hazards
6.1 Pressure relief
Under several possible conditions of malfunction, high pressures can occur in parts of the system and mechanical relief devices are advised or mandatory. The standard form of relief valve is a spring-loaded plunger valve.
The rules to remember:
- No shut-off valve is permitted between the relief valve and the vessel it protects, unless two such valves are fitted, when the shut-off may isolate one at a time.
- Two valves are required on a vessel greater than 285 litres in volume.
- The outlet of the valve must be led to the open air, in a location where the sudden discharge of refrigerant will not cause annoyance or danger.
- Under certain circumstances, a relief valve from the high-pressure side may enter the low side of the same system.
- Small vessels may have a plug of a low melting point metal, which will melt and release the pressure in the event of fire.
- Plunger-type relief valves, if located outdoors, should be protected from the ingress of rain, which may corrode the seat. Steel valves, when installed, should have a little oil poured in to cover the seat as rust protection.
- To prevent overpressure within a compressor, a relief valve or bursting disc is often fitted between the inlet and discharge connections.
Nickel, 0.05 mm thick, fitted between compressor discharge and suction. A ruptured disc is indicated by suction and discharge pressures being about equal.
6.2 Liquid carry-over and hydraulic shock
Although compressor valves are intended to handle only dry gas, liquid refrigerant or traces of oil may sometimes enter the cylinder and must pass out through the discharge valves. These may be arranged on a spring-loaded head, which will lift and relieve excessive pressures. Some makes also have an internal safety valve to release gas pressure from the discharge back to the suction inlet.
Protection devices against liquid carry-over:
- Spring-loaded discharge valve retainer — lifts to give extra valve lift if liquid is discharged
- Spring-loaded discharge valve cage — lifts on liquid carry-over
- Nickel bursting disc between discharge and suction
- Solenoid liquid stop valve which shuts just before the machine cuts out, so the compressor clears the suction line before stopping — this prevents liquid knock when restarting
- Master solenoid on large systems, closing on a fault to prevent flooding
- Low-pressure receiver / suction separator / accumulator — the safety vessel which prevents liquid entering the compressor
Spring-loaded safety plate on rotary vane compressors, to relieve excess pressure if liquid refrigerant enters.
6.3 Compressor overpressure and overheating
- Cylinder relief valves and over-pressure cut-outs are standard practice fittings.
- A differential oil pressure switch and an overload electrical switch protect the machine from low oil or high vapour pressure.
- Compressors should not be run too hot, otherwise there is a danger of oil vaporisation and subsequent ignition by the heat of compression.
- Compressors will tend to overheat under low mass flow conditions resulting from abnormally low suction pressures or lengthy running with capacity reduction. Detectors may need to be fitted to warn against this condition.
7. Electrical Safety
- Semi-hermetic compressors: induction motors only can be used, with any starting switches outside the crankcase, since any sparking would lead to decomposition of the refrigerant. Electrical leads pass through ceramic or glass seals.
- The failure of an inbuilt motor will lead to products of decomposition and serious contamination of the system, which must then be thoroughly cleaned.
- Electrical faults are responsible for a large number of refrigerator problems. Ship vibration is the reason for many of the electrical faults — loose connections, broken wires and earths from chafed insulation.
- Electrical isolation permit must be obtained, and the local electrical panel circuit breaker put off, before any work on the machine.
- The compressor must be removed from auto start and from priority before work begins.
8. Safe Isolation — The Mandatory Sequence
Why each step:
| Step | Why |
|---|---|
| Pump down first | Removes refrigerant from the section to be opened, so it can be opened at low pressure and with minimal loss |
| Cooling water 30 minutes | Ensures the condenser is fully cooled and the refrigerant has condensed and collected, so the pressure reading is meaningful |
| Electrical isolation with permit | The only positive protection against the machine starting while someone is inside it |
| Valves shut and tagged | Prevents refrigerant entering the opened section |
| Removed from auto/priority | Prevents a remote control system restarting the machine |
| "Man at work" board | Warns every other person on board |
9. Handling Suspect Oil
Overheating or an electrical fault in the winding of a hermetic or semi-hermetic compressor motor will produce contaminants, including the halogen acids, which can be detected by their acrid smell, litmus paper or other tests.
Eye goggles and rubber gloves should be worn when handling such suspect oil. If shown to be acid, the oil must be removed and carefully disposed of, and the system thoroughly cleaned out.
The condition of the compressor oil is a direct indication of the physical and chemical cleanliness of the system. The oil as seen through the crankcase sight glass should remain transparent. If it takes on a white, emulsified appearance it is wet and should be drained and discarded.
10. Brine Room and Cold Room Safety
10.1 Brine rooms
There is a possibility that the air content of brine rooms could become explosive or inflammable under conditions of hydrogen gas liberation due to corrosive action; it is advisable not to allow naked lights.
Brine handling:
- Brine is calcium chloride (CaCl₂) solution, or sodium chloride with about 1 % caustic soda added.
- It should be maintained in an alkaline state, checked with litmus paper or phenolphthalein.
- Brine density is taken by hydrometer at 15.5 °C, and the brine header tank checked for leakage.
- Brine is corrosive and will damage eyes and skin — wear PPE when sampling or topping up.
10.2 Cold room entry
- Cold room temperatures are typically 4–5 °C for vegetable and dairy rooms — cold enough for hypothermia over a prolonged period, and cold enough for slips from condensation.
- Never enter a cold room and let the door close behind you. Use the internal alarm/escape device.
- If refrigerant has leaked into a cold room, it will be at floor level and the space is a confined space — do not enter without BA.
- Frost on floors is a slip hazard; frost on coils is a defrost-maintenance issue.
10.3 Legionella (air conditioning)
Legionella bacteria is a type of pneumonia which may be fatal to older people, and its presence has been associated with the air conditioning plant of large buildings. There is a risk that the bacteria could flourish in the air conditioning systems of ships and consequently a Department of Transport M Notice has been issued to give warning and to recommend preventative measures.
Organisms breed in stagnant water or in wet deposits of slime/sludge. Possible locations: air inlet area and below the cooler, the filter, water spray type humidifiers, and exposed insulation.
Preventative measures:
- Provision of adequate drainage to remove stagnant water.
- Weekly inspection and cleaning as necessary of filters with a 50 p.p.m. super-chlorinated solution.
- The solution to be used on the cooler drain area at not more than three-month intervals.
- Regular sterilization with water spray type humidifiers — steam humidifiers being preferred.
Reference: Merchant Shipping Notice no. M1215 (1986), Contamination of Ships' Air Conditioning Systems by Legionella Bacteria.
11. Fire and Emergency Response
| Situation | Action |
|---|---|
| Refrigerant leak in an enclosed space | Do not enter without BA. Ventilate. Raise the alarm. Isolate the section if safe to do so. Account for personnel |
| Ammonia leak | Evacuate; BA only; wet cloth to the face only as a last resort; shut down and isolate; ventilate; water spray to knock down vapour |
| Fire involving a halocarbon plant | Breathing apparatus mandatory — decomposition products (chlorine, phosgene) are more dangerous than the refrigerant. Cool adjacent cylinders. Consider evacuation of the space |
| CO₂ cylinder overheating | The safety disc will rupture and release the gas. Cool the cylinder if it can be done from a safe position; otherwise evacuate the area |
| Ruptured bursting disc | Suction and discharge pressures about equal. Stop the machine, renew the disc, and investigate why it ruptured |
| Liquid refrigerant on skin or eyes | Flush with copious lukewarm water; do not rub; seek medical attention for eyes |
| Suspect oil (acidic, acrid) | Goggles and rubber gloves; remove and dispose of carefully; clean out the system |
| Man collapsed in a cold room or brine room | Treat as confined space rescue — BA, harness, second man, no lone entry |
12. Environmental Obligation
- Never release refrigerant to atmosphere as a routine practice.
- CFCs are banned for servicing existing plants, and virgin HCFCs are banned for plant servicing under the Montreal Protocol and the EC dates in force.
- Recover refrigerant into a cylinder when charging down, purging or removing an overcharge — connect the collecting cylinder to the purging line of the condenser, open the valve and collect the air/gas in the cylinder.
- Remember TEWI: the energy-consumption term usually dominates the global warming impact of a plant. Keeping the condenser clean and the condensing pressure low is an environmental measure, not just an economic one.