Safety on the Oily Water Separator
The hazards specific to this plant, and the controls that answer them.
Key Principles at a Glance 6 points
- The hazards are both physical and legal: overpressure of the separator, accidental discharge overboard, siphon discharge, fire risk during monitoring, pollution from routine operations and bunkering spillage.
- The relief valve protects the vessel and must discharge to the pump suction or an overflow tank — never to a confined space and never overboard, because a lifting relief valve in the wrong place is a hazard of its own.
- The pollution hazard is the one no amount of engineering eliminates, because it depends on discipline rather than on a component.
- The exposure is personal: the fines for discharging over the limit fall on named individuals — the operating engineer, the Chief Engineer and the Master — and not only on the company.
- On a tanker, the fibre optic arrangement is what keeps the monitor's lamp and photo-cell out of the hazardous pump room.
- Housekeeping is a control, not housekeeping: oil left in the machinery space is a slip hazard, a fire load, and the reason a small leak becomes a serious casualty.
1. The hazards and their controls
The SMS, the class rules, the M Notices and the Chief Engineer's orders override. The overboard valve is opened only in the presence of the Chief Engineer and is relocked afterwards. Never discharge oil outside the regulation.
| Hazard | Control |
|---|---|
| Overpressure of the separator | A relief valve, discharging to the pump suction or to an overflow tank — never to a confined space and never overboard. Setting, location and number of valves: Inside the Separator, 5 |
| Accidental discharge overboard | The overboard valve chained and locked with the key with the Chief Engineer, and the bilge connection blanked by a blind flange. A discharge is legal only on passage, outside the prohibited distance, with the monitor running |
| Siphon discharge when the separator is stopped | A siphon breaker, anti-siphon valve or vented loop in the discharge line — Inside the Separator, 6 |
| Fire risk during monitoring | The oil discharge monitor relies on a photo-cell and a lamp. Tanker sampling equipment is made safe by fibre optics, keeping the light source and the cell out of the pump room |
| Oil pollution from routine operations | No oil leak is tolerated. The practice is in The Bilge System, 6; why it is a safety control is in section 5 below |
| Bunkering spillage | Scuppers plugged, drip trays under the ship-shore connection, the blank secured at the opposite end of the crossover. The full list is in The Bilge System, 5 |
| Personnel safety at the overboard valve | The valve is opened and shut only in the presence of the Chief Engineer, and relocked with the key returned afterwards |
| Environmental and regulatory | Never discharge oil outside the regulation. Record every discharge with quantity, time and position. Keep the MARPOL certificate copy, the oil disposal receipts, the dirty oil and sludge piping diagram and the USCG notice with the Oil Record Book |
2. The pressure hazard
The separator is a pressure vessel working at about 2 bar, and it is normally unattended once running. The relief valve is therefore the only protection against a blockage downstream turning the vessel into an overpressure case. The valve itself — its setting, the requirement that one be fitted on each stage, and the arrangement of the pipework — is described with the rest of the machine in Inside the Separator, section 5.
What belongs in a safety chapter is where it discharges. Correctly led, a lifting relief valve is an inconvenience and nothing more. Led to a confined space, or overboard, it becomes a hazard of its own: it puts hot oily water where people are working, or into the sea, at the exact moment something else has already gone wrong. A relief valve found discharging anywhere other than the correct place is a defect to be raised, not a quirk of the installation.
3. The pollution hazard
This is the hazard that no amount of engineering eliminates, because it depends on discipline rather than on a component.
The controls are administrative as much as mechanical, and each one belongs to another chapter. The overboard valve under chain and lock with the key held by the Chief Engineer, and the bilge connection blanked by a blind flange, are in The Bilge System, section 4. The siphon breaker is in Inside the Separator, section 6. The rule that the monitor, the alarm and the 15 p.p.m. stopping device are never bypassed is in Oil Content Monitoring. The recording of every discharge, with quantity, time and position and three signatures, is in When You May Discharge, section 6.
What makes this a safety subject rather than a compliance one is that the exposure is personal. The fines for discharging over the limit fall on named individuals — the operating engineer, the Chief Engineer and the Master — and not only on the company. The discipline exists because the consequences are attached to people.
4. Fire and explosion
The separator itself handles oil and water at moderate temperature, so it is not in itself a major fire risk. Two related risks are real.
The monitor's lamp and photo-cell. In a machinery space this is unremarkable. In a tanker the sampling equipment sits in the pump room, which is a hazardous area, and the fibre optic arrangement described in Oil Content Monitoring, section 5 is what keeps the light source and the cell out of it.
The incinerator that burns the sludge. A waste oil burner is a genuine fire risk, and its emergency fuel shutdown valve, furnace door interlock and cooling fan exist for that reason. The unit and its safety devices are dealt with in Oily Sludge and Its Disposal, section 4. The one point that belongs here is that the purge before lighting is a safety step and not a warm-up — skipping it is how furnaces are damaged and how a flashback reaches the waste oil line.
5. Housekeeping as a safety measure
The practice itself — no oil leak tolerated, trays and drip pans and valve glands kept clean, the tank top and bilges hosed down frequently — belongs to The Bilge System, section 6, because its first purpose is to keep the oil out of the bilge water in the first place.
What makes it a safety item as well is the second-order consequence. Oil that stays in the machinery space is a slip hazard on the tank top and the floor plates, it is a fire load spread across hot surfaces and exhaust lagging, and it is the reason a small leak becomes a serious casualty — a bilge that is already full of oil cannot be used to take the water from a real one. On this plant, cleanliness is a control, not housekeeping.