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Vapour given off by a flammable liquid while carrying at sea

Vapour given off by a flammable liquid will burn when ignited provided it is mixed with certain proportions of air, or more accurately with the oxygen in air. But if there is too little or too much vapour compared to the air, so that the vapour-and-air mixture is either too lean or too rich, it will not burn.

The limiting proportions, expressed as a percentage by volume of flammable vapour in air, are known as the lower flammable limit (LFL) and the upper flammable limit (UFL), and the zone, in between is the flammable range. The range of flammable vapour concentrations in air between the lower and (Explosive Range) upper flammable limits. Mixtures within this range are capable of being ignited and of burning.

Combustion of a vapour-and-air mixture results in a very considerable expansion of gases which, if constricted in an enclosed space, can raise pressure rapidly to the point of explosive rupture. In addition, a flammable liquid must itself be at or above a temperature high enough for it to give off sufficient vapour for ignition to occur. This temperature is known as the flash point.

Some cargoes evolve flammable vapour at ambient temperatures, others only at higher temperatures or when heated. Safe handling procedures depend upon the flammability characteristics of each product. Non-combustible cargoes are those which do not evolve flammable vapours.

Modern Chemical tanker underway

The fire risk presented by a flammable cargo depends upon the oxygen content of the atmosphere above it. By filling the ullage space in a cargo tank with an inert gas such as nitrogen or the output of an oil fired inert gas generator, the oxygen content can be reduced to a level at which the atmosphere will no longer support combustion of flammable vapour. This is known as inerting a tank.

But it is important to remember that an inerted atmosphere may become flammable again if air is admitted, for instance during routine measuring or on venting the mixture to atmosphere or during gas freeing with air

An inert atmosphere must not be considered as being without hazard, however, as without enough oxygen it will not support life either. Any person entering a tank which has been inerted must always follow strict procedures for entry into enclosed spaces.

Related info

  1. Toxicology and associated hazards onboard chemical tankers

  2. Toxicity is the ability of a substance, when inhaled, ingested, or absorbed by the skin, to cause damage to living tissue, impairment of the central nervous system, severe illness or, in extreme cases, death. The amounts of exposure required to produce these results vary widely with the nature of the substance and the duration of exposure to it. ....

  3. Hazards of vapour given off by a flammable liquid while carrying at sea

  4. Vapour given off by a flammable liquid will burn when ignited provided it is mixed with certain proportions of air, or more accurately with the oxygen in air. But if there is too little or too much vapour compared to the air, so that the vapour-and-air mixture is either too lean or too rich, it will not burn. ....

  5. Reactivity of various noxious liquid chemicals

  6. Self-reaction: The most common form of self-reaction is polymerisation. Polymerisation generally results in the conversion of gases or liquids into viscous liquids or solids. It may be a slow, natural process which only degrades the product without posing any safety hazards to the ship or the crew, or it may be a rapid, exothermic reaction evolving large amounts of heat and gases. .....

  7. Most corrosive chemicals carried onboard chemical tankers

  8. Acids, anhydrides and alkalis are among the most commonly carried corrosive substances. They can rapidly destroy human tissue and cause irreparable damage. They can also corrode normal ship construction materials, and create a safety hazard for a ship.....

  9. Posoning hazards & first aid treatment

  10. The poison is a very toxic substance which when absorbed into the human body by ingestion, skin absorption, or inhalation produces a serious or fatal effect. Poison may enter the human body orally, by inhalation, or by skin contact. After being absorbed by the body it may affect certain organs or give a general poisonous effect. Lately the cancerogene effects of some industrial chemicals have been noticed. This has led to significant reductions of hereto accepted TLV- values in many countries.....
  11. Specific gravity,Vapour pressure and boiling point,Electrostatic charging & measuring Viscosity
  12. Tanks on a Chemical Tanker are normally designed to load cargoes of a higher specific gravity than an oil tanker. Very often the design strength differs between groups of tanks on the same ship. ....

  13. General precautions onboard chemical tankers

  14. Additional precautions for specific cargoes are necessary and should also be incorporated in the ship’s cargo handling procedures....

  15. Mooring precautions onboard chemical tankers

  16. The consequences of a chemical tanker ranging along a jetty or breaking away from a berth could be disastrous, especially during a cargo transfer involving multiple different chemicals. Correct and sufficient mooring is therefore of the utmost importance.

  17. Berth precautions onboard chemical tankers

  18. If an unauthorised craft comes alongside or operates in an area which may create a danger, it should be reported to the port authority and, if necessary, cargo transfer operations should cease. .....

  19. Cold weather countermeasures, avoiding electric storms

  20. During cold weather, precautions should be taken to prevent equipment and systems from freezing. Attention should be given to pneumatic valves and control systems, fire lines and hydrants, steam driven equipment, cargo heating systems, pressure/vacuum valves etc......

  21. Restriction on using radio equipments and other mobile devices in cargo working areas

  22. During medium and high frequency radio transmissions significant energy is radiated, which can create a danger of incendive sparking by inducing an electrical potential in unearthed steelwork.

  23. Securing cargo tank lids and required safety precautions

  24. Improper closing and sealing of cargo tank hatches can be a major cause of cargo contamination. A properly closed and sealed tank hatch/opening will prevent sea water ingress and maintain a positive pressure Nitrogen blanket in the ullage space. ....

  25. Means of access (gangways or accommodation ladders) safety precautions

  26. Emergency towing-off wires ( fire wires) ,Ship’s readiness to move Deckhouses and superstructures safety precautions .....

  27. Precautions against static electricity

  28. Static electricity is generated by friction that occurs between different materials during relative motion. Electrostatic charges can then accumulate in materials which are poor conductors of electricity or which are good conductors but are insulated.....

  29. Cargo tank entry safety precautions

  30. On chemical tankers the entry of personnel into cargo tanks is a more common practice than on oil tankers as a result of the requirement for inspections between grades etc; despite this, it is essential that the necessary checks are conscientiously made and recorded prior to entry in order to ensure the safety of personnel, enclosed space rescue equipment must be made ready for immediate use. .....

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