Oil Content Meter & Bilge Alarm Calibration in Gioia Tauro.

Oil content meter and 15 ppm bilge alarm calibration

Oil content meter and bilge alarm calibration confirms that the 15 ppm bilge alarm fitted to the oily water separator (OWS) reads accurately, alarms at the right point and stops overboard discharge when it should. The alarm is the last barrier between machinery-space bilge water and the sea, and its records are what inspectors use to judge whether the ship has discharged legally.

A drifting monitor or a three-way valve that does not change over can put the ship in breach of MARPOL, with serious consequences for owners and crew. vslSafety coordinates maker-authorised technicians to calibrate, test and certify the system during the port call.

Regulatory requirements and who can calibrate

MARPOL Annex I regulation 14 requires ships of 400 gross tonnage and above to carry oil filtering equipment. Ships of 10,000 gross tonnage and above need equipment with an alarm and automatic stopping so discharge stops when the effluent exceeds 15 ppm. Regulation 15 sets the discharge conditions, including the 15 ppm limit with the equipment in operation.

The performance standard is resolution MEPC.107(49), which applies to installations on ships whose keels were laid on or after 1 January 2005, and to new installations on older ships as far as reasonable. Older installations may still comply with resolutions A.393(X) or MEPC.60(33). The key requirements for 15 ppm bilge alarms are:

• An alarm pre-set by the manufacturer to activate above 15 ppm, and also on failure, warm-up or loss of power
• A response time of not more than 5 seconds
• Recording of date, time, alarm status and separator operating status, stored for at least 18 months
• Tamper protection: any access beyond basic drift and zero checks requires breaking a seal, and the alarm must activate whenever clean water is used for cleaning or zeroing

Paragraph 4.2.11, replaced by resolution MEPC.285(70) in 2016, requires the accuracy to be checked by calibration and testing by the manufacturer or persons authorised by the manufacturer. This must be done at intervals not exceeding five years after commissioning, or within the term in the maker’s instructions if shorter. Alternatively, the unit may be replaced by a calibrated alarm. The calibration certificate must be kept on board, and its validity is checked at IOPP annual, intermediate and renewal surveys.

Calibration and check intervals

Item	Requirement	Interval	Reference
15 ppm bilge alarm accuracy	Calibration and testing by maker or maker-authorised person, or replacement by a calibrated unit	Not exceeding 5 years, or shorter if the maker specifies	MEPC.107(49) 4.2.11, as amended by MEPC.285(70)
Calibration certificate	Validity checked	Annual, intermediate and renewal IOPP surveys	MEPC.107(49) 4.2.11
Alarm data record	Date, time, alarm and operating status retained	At least 18 months	MEPC.107(49) 4.2.9
Drift, repeatability and zero	Simple onboard check to maker’s instructions	Per maker and planned maintenance system	MEPC.107(49) 4.2.8

What the service includes

• Identification of alarm, measuring cell, software version, separator and stopping arrangement against the type-approval certificate
• Check of seals and tamper protection, with any broken seal recorded
• Cleaning and inspection of the measuring cell, sample line, flushing water supply, solenoid valves and sample pump
• Calibration and accuracy check with maker-approved reference fluids or tools, or exchange for a factory-calibrated cell or unit
• Functional test of the 15 ppm alarm, time delay and fail-safe alarm on loss of power or sample flow
• Test of the automatic stopping device or three-way valve, recirculation and position feedback
• Download and check of the data record and its 18-month storage
• Calibration certificate and service report, with new seals fitted

Equipment types covered

Providers work on stand-alone 15 ppm bilge alarms and those supplied with a separator package. Examples include Rivertrace and Deckma monitors, and alarms fitted to separators from makers such as Alfa Laval, RWO and Marinfloc. Some makers calibrate on board with reference fluids; others require the measuring cell or complete unit to be exchanged for a calibrated one, which MEPC.107(49) allows. Oil discharge monitoring equipment (ODME) on tankers is a separate system approved under resolution MEPC.108(49) and needs its own specialist. See also our calibration services.

Common defects and PSC deficiencies

• No valid calibration certificate on board, or one older than five years or the maker’s term
• Broken or missing seals, or signs that the sample line has been altered or supplied with fresh water
• Alarm not working on test, or the three-way valve not changing over to recirculation
• Data record not available for the last 18 months, or the time clock set wrongly
• Fouled measuring cell giving false alarms, leading crew to bypass the system
• Oil Record Book Part I entries that do not match the alarm record or the separator running hours
• Unauthorised connections to the overboard line, which PSC officers look for when they trace the piping

Many operators combine the calibration with a pre-PSC inspection.

Certificates and documents you receive

The technician issues a calibration certificate stating the alarm model, serial number, date of calibration, method or reference used, readings found and left, and the next due date, together with the service company’s maker authorisation. A service report records seal numbers, any parts replaced and outstanding defects. Keep the certificate with the type-approval certificate and the IOPP supplement for the surveyor and PSC.

How to prepare the vessel

Check the certificate date early, as makers often supply calibrated exchange cells from stock at their own stations and delivery can take time. Have clean water available for flushing and, if the separator must be run, enough water in the bilge holding tank and permission to operate or recirculate in port. Where ports ban discharge, test in recirculation. Report known faults in advance so the technician brings spares.

Information needed for a quotation

• Vessel name, IMO number, flag and class
• Port, ETA and ETD, and IOPP survey due date
• Bilge alarm maker, model, serial number and software version
• Separator maker and model, and type of stopping device
• Date and copy of the last calibration certificate
• Current fault or alarm history, and spares on board
• Whether the separator can be run, and whether class attendance is needed

vslSafety coordinates a maker-authorised provider at the vessel’s port and confirms whether calibration will be on board or by exchange unit.

Frequently asked questions

How often must a 15 ppm bilge alarm be calibrated?

Under MEPC.107(49) as amended by MEPC.285(70), accuracy must be checked by calibration and testing at intervals not exceeding five years after commissioning, or within the maker’s term if that is shorter. The certificate’s validity is checked at every annual, intermediate and renewal IOPP survey, so an expired certificate is quickly noticed. Check the maker’s manual, as some specify shorter periods.

Can the crew calibrate the bilge alarm?

No. The guidelines say accuracy checks can only be done by the manufacturer or persons authorised by the manufacturer. The crew may carry out simple drift, repeatability and zero checks if the maker provides a means, but any access beyond that requires breaking a seal. A certificate from an unauthorised workshop may not be accepted by the surveyor.

Can we replace the unit instead of calibrating it?

Yes. MEPC.107(49) allows the alarm to be replaced by a calibrated 15 ppm bilge alarm, and many makers supply a calibrated measuring cell or complete exchange unit with a certificate. Make sure the replacement matches the type-approved configuration, and that the last 18 months of data remain available on board after the swap.

What do PSC officers check on the OWS and bilge alarm?

They usually check the calibration certificate, seals, a live test of the alarm and stopping device, the data record, and whether the Oil Record Book matches. They may trace the overboard piping looking for bypasses. A working alarm with poor records can still lead to a deficiency or detention, so procedure matters as much as calibration.