Tanker and Terminal Hazards

Tanker and terminal hazards the reasons the practices adopted to ensure safety in operations, all personnel should be familiar with the flammable prop

Hazards of Petroleum In order to appreciate the reasons for the practices adopted to ensure safety in tanker and terminal operations, all personnel should be familiar with the flammable properties of petroleum, the effects of the density of petroleum gases and their toxic properties. Contains a brief summary and more detailed information is given in next post.

I. FLAMMABILITY
When petroleum is ignited, it is the gas progressively given off by the liquid which burns as a visible flame. The quantity of gas available to be given off by a petroleum liquid depends on its volatility which is frequently expressed for purposes of comparison in terms of Reid vapour pressure (RVP). A more informative measure of volatility is the true vapour pressure but unfortunately this is not easily measured. It is referred t in this guide only in connection with venting problems associated with very volatile cargoes, such as some crude oils and natural gasolines.

Petroleum gases can be ignited and will burn only when mixed with air in certain proportions If there is too little or too much petroleum gas the mixture cannot burn. The limiting proportions, expressed as percentage by volume of petroleum gas in air, are known as the lower and upper flammable limits. They vary amongst the different possible components of petroleum gases. For the gas mixtures from the petroleum liquids encountered in normal tanker practice the overall range is from a minimum lower flammable limit of about 1% gas by volume in air to a maximum upper flammable limit of about 10% gas by volume in air.

As a petroleum liquid is heated the concentration of gas in air above it increases. The temperature of the liquid at which concentration, using a specific measuring technique, reaches the lower flammable limit is known as the flashpoint of the liquid

 
II. FLAMMABILITY CLASSIFICATION
There are many classification systems defining the flammability characteristics petroleum liquids, most of which are based o flashpoint and Reid vapour pressure data. For the purpose of this guide, which deals only with the particular conditions in petroleum tanker cargo handling, the division of such liquids into the two broad categories non-volatile and volatile, as defined below, is in general sufficient to ensure that proper precautions can be specified.

Non-Volatile
Flashpoint of 60 deg.C or above as determined by the closed cup method of testing.

Volatile
Flashpoint below 60 deg.C as determined by the closed cup method of testing

If there is any doubt as to the characteristics of a cargo, or if a non-volatile cargo is being handled at a temperature above its flashpoint minus 10 deg.C, it should be treated as volatile petroleum. Owing to their particular characteristics, residual fuel oils should always be treated as volatile.

III. GAS DENSITY
The gases from normal petroleum liquids are heavier than air and inert gas, thus the possibility of layering of gases is very important in cargo handling operations. The density of the undiluted gas from a high vapour pressure distillate, such as motor gasoline, is likely to be about twice that of air and about 1.5 times that from a typical crude oil. These density differences diminish as the gases are diluted with air. Flammable mixtures usually contain at least 90% by volume of air and consequently have densities almost indistinguishable from that of air. More detailed information on the density of petroleum gases is given in next update.

IV. TOXICITY
Comparatively small quantities of petroleum gas when inhaled can cause symptoms of diminished responsibility and dizziness similar to drunkenness, with headache and irritation of the eyes. The inhalation of a sufficient quantity can be fatal. These symptoms can occur at concentrations well below the lower flammable limit. However, petroleum gases vary in their physiological effects and human tolerance to these effects also varies widely. It should not be assumed that because conditions can be tolerated the gas concentration is within safe limits.

The smell of petroleum gas mixtures is very variable, and in some cases the gases may dull the sense of smell. The impairment Of smell is especially likely and particularly serious if the mixture contains hydrogen sulfide. The absence of smell should never be taken to indicate the absence of gas. More detailed information on the toxic properties of petroleum, and of substances associated with the carriage of petroleum, is given in detail next post.

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• 1. LNG Cargo ship
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• 2. ISGOTT 5th Edition - International Safety Guide for Oil Tankers and Terminals
• 3. Single Point Mooring Maintenance and Operations Guide SMOG 2015
• 4. Guidelines for Offshore Tanker Operations, OCIMF 1ed. 2018