NIMASA STCW Tanker Familiarization key terms

The lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture with air near its surface. Cargoes with low flashpoints release flammable vapour at normal ambient temperatures and need strict ignition control.

The band of vapour concentrations in air between the lower and upper flammable limits within which ignition produces a flame. Below the lower limit the mixture is too lean to burn; above the upper limit it is too rich.

The temperature at which a flammable vapour-air mixture ignites spontaneously without any external spark or flame. It explains why hot work, exhaust manifolds and steam lines can ignite cargo vapour without an obvious ignition source.

The mass of a cargo vapour compared with the same volume of air. Petroleum vapours are heavier than air and collect in bilges, cargo tanks and low spaces, so gas detection and ventilation must target the bottom of a compartment.

Any spark, flame, hot surface or energy release able to ignite a flammable mixture. On tankers it includes naked flames, smoking, hot work, electrical equipment, engine exhausts and electrostatic discharge, all of which must be controlled.

Electric charge that builds up on surfaces or in liquids and can discharge as a spark. Splash filling, mist from water washing, steam and synthetic clothing all generate charge, so bonding and controlled flow rates are essential.

Electrically connecting metallic components so they sit at the same potential and cannot spark against each other. Cargo hoses, loading arms and portable equipment are bonded to the ship before transfer begins and stay connected until it ends.

Loading cargo by dropping it freely into a nearly empty tank, which creates mist and heavy static generation. It is avoided by keeping the fill line submerged and using reduced initial flow rates until the line is covered.

Equipment that supplies oxygen-depleted flue gas or nitrogen to cargo tanks to keep the atmosphere below the flammable range. It maintains positive pressure and a low oxygen content during loading, discharge, ballasting and tank cleaning.

The percentage of oxygen in a tank atmosphere, measured by a calibrated oxygen analyser. Inerting normally targets 8 percent or less by volume, and the reading must be confirmed before any operation that could admit air.

The use of calibrated portable or fixed instruments to measure flammable vapour, oxygen, and toxic gases such as hydrogen sulphide or benzene. Readings are recorded and repeated at intervals throughout cargo and enclosed-space operations.

Displacing an unwanted gas from a tank using an inert gas or another gas until the required atmosphere is reached. Purging may be done to remove hydrocarbon vapour before gas-freeing or to prepare a tank for a different cargo.

Deliberately replacing a tank atmosphere with fresh air so the space is safe for entry or hot work. It follows purging and requires confirmed readings of flammable vapour, oxygen and toxicity before entry is permitted.

Entering an enclosed or poorly ventilated space such as a cargo tank, cofferdam or pump room. It requires a written permit, atmosphere testing, ventilation, a standby person outside and a planned rescue arrangement.

A formal written authorisation for welding, cutting, grinding or other spark-producing work. It confirms gas-freeing, atmosphere testing, removal of combustible material, fire watch and standby firefighting equipment before work starts.

A joint checklist completed and signed by ship and terminal representatives before cargo transfer begins. It covers moorings, communications, emergency stop, firefighting equipment, bonding, vapour control and agreed transfer rates.

The agreed volume of cargo transferred per unit time. The initial rate is kept low to test lines and limit static generation, and maximum rates are set by venting capacity, cargo line size and shore arrangements.

The final slow stage of loading, with tanks nearly full. Rates are reduced, high-level alarms and tank gauging are watched closely, and communication with the terminal is maintained to prevent overflow.

Systems and procedures that stop a cargo tank being filled beyond its safe limit. They include high-level alarms, independent overflow sensors, tank gauging, agreed topping-off rates and a tested emergency stop.

A rapid, prearranged stop of cargo transfer, usually by a single agreed signal or button. It closes valves, stops pumps and isolates the transfer to limit spillage or fire risk, and is tested during the ship/shore checklist.

An empty space between two tanks, or between a cargo tank and a machinery or accommodation space, that acts as a buffer. It is monitored for leaks and must never be used to carry cargo.

A hull arrangement with an inner hull forming cargo tank boundaries and an outer hull, leaving ballast or void spaces between them. It reduces the risk of cargo escaping after grounding or collision.

The compartment that holds liquid cargo. Its type and material depend on the cargo: integral or independent tanks on gas carriers, and coated or stainless steel tanks on chemical tankers to resist corrosion.

A space containing cargo pumps, valves and pipelines, often below deck. Because it can accumulate heavy flammable vapour, it is treated as an enclosed space with fixed gas detection, ventilation and restricted entry.

A pressure/vacuum valve that lets a cargo tank breathe in or out within set limits, preventing overpressure or vacuum damage during loading, discharge and temperature change. It must be correctly set and kept operational.

A pipeline carrying displaced cargo vapour from the ship's tanks back to the shore terminal during loading. It reduces vapour release to atmosphere and must be connected and checked before transfer starts.

Systems and procedures that prevent cargo vapour escaping to atmosphere, including vapour return lines, closed loading and vapour recovery units. They protect the environment and reduce fire and health hazards on deck.

Organic chemicals that evaporate readily from cargo and contribute to air pollution and smog. Their release is limited by vapour emission control, closed sampling and careful tank gas management.

The capacity of a substance to harm health through inhalation, skin contact or ingestion. Cargoes such as benzene, hydrogen sulphide and some chemicals can cause acute poisoning or long-term illness, so exposure limits and PPE are enforced.

Threshold Limit Value: the airborne concentration of a substance considered safe for repeated occupational exposure over a working lifetime. It guides ventilation, monitoring and respirator selection for cargo vapours.

A highly toxic, flammable gas with a rotten-egg smell that occurs in some crude oils and cargoes. It deadens the sense of smell at higher concentrations and can kill quickly, so detection and escape sets are essential.

Clothing and equipment worn to protect against cargo hazards, such as chemical suits, gloves, goggles, helmets and breathing apparatus. Selection depends on the cargo's safety data sheet and the task being performed.

A document giving the hazards, physical properties, health effects, protective measures and emergency actions for a cargo. It must be available on board before the cargo is loaded and is used to plan safe handling.

The older name for the safety data sheet supplied by the manufacturer or shipper. It carries the same information on hazards, first aid, firefighting and spill response and remains a key reference for chemical cargoes.

The International Convention for the Prevention of Pollution from Ships. Its annexes regulate oil, noxious liquid substances, harmful packaged goods, sewage, garbage and air pollution, and underpin tanker discharge and record-keeping rules.

A mandatory record of oil cargo and machinery-space operations such as loading, discharge, ballasting, tank cleaning and disposal. Entries are signed and can be inspected by port state control.

A required log of operations involving noxious liquid substances on chemical tankers, including loading, unloading, tank cleaning and discharge of residues. It supports compliance with MARPOL Annex II and prewash requirements.

The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers. It sets minimum competence, training and certification requirements, including basic and advanced tanker training for crew serving on tankers.

Basic training required for all seafarers assigned duties on tankers, covering tanker types, cargo hazards, safety, pollution prevention and emergency procedures. It must be completed before taking up tanker duties.

Further STCW training for officers and others with immediate responsibility for cargo operations. It covers detailed cargo handling, stability, inert gas, emergency response and pollution prevention for the tanker type concerned.

The International Safety Guide for Oil Tankers and Terminals, a widely used industry reference. It gives recommended practice for cargo handling, inert gas, fire protection, ship/shore liaison and safe entry into tanks.

The International Convention for the Safety of Life at Sea. It covers ship construction, fire protection, life-saving appliances, carriage requirements and emergency procedures that apply to tankers as well as other ships.

The International Safety Management Code, requiring a safety management system with documented procedures, risk assessment and emergency preparedness. Tanker operators use it to control cargo, pollution and safety risks.

A prepared set of responses for incidents such as fire, collision, spillage or cargo release. It assigns duties, lists equipment and contacts, and is exercised through drills so the crew can act quickly under pressure.

The assembly of crew at designated stations following an alarm. Muster lists assign each person a role, and head counts and reports to the bridge confirm that everyone is accounted for.

A planned practice of an emergency procedure, such as firefighting, abandon ship, oil spill response or enclosed space rescue. Drills test competence, equipment and communication and are recorded in the ship's log.

The recovery of a person from a tank or other enclosed space. Rescuers must not enter unprotected; they use breathing apparatus, harnesses and rescue lines, with a standby team and permit controlling the operation.

A formal control document authorising a specific high-risk task for a set period under stated precautions. It is used for hot work, enclosed space entry, working aloft and other tasks needing isolation and verification.

A ship designed to carry cargoes kept liquid by pressure, refrigeration or both, such as LPG, LNG and ammonia. Cargo is carried in independent or integral tanks with reliquefaction or boil-off management.

Cargo vapour produced by heat entering refrigerated tanks. It is removed by reliquefaction, burned in the ship's boilers or engines as fuel, or vented only under strictly controlled conditions.

A tanker built to carry liquid chemicals in bulk, with tank coatings or stainless steel and segregated piping to prevent contamination and corrosion. Cargoes are classified by hazard under MARPOL Annex II.

Ballast water carried in tanks permanently separated from the cargo system and fuel oil. It avoids contaminating ballast with oil, allowing cleaner ballast discharge and reducing operational pollution risk.

Cleaning cargo tanks with high-pressure crude oil during discharge to remove clingage and reduce residues. It is controlled by strict procedures to limit static generation and is recorded in the Oil Record Book.

The design and equipment measures on gas carriers to detect and control fire, including dry powder systems, water spray, gas detection and emergency shutdown. They reflect the high flammability of liquefied gas cargoes.

Checking that a cargo is suitable for the ship's tanks, coatings, gaskets and piping, and will not react dangerously with residues of a previous cargo. It is confirmed from the safety data sheet and cargo list before loading.