Chapter 1
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. This Chapter contains a brief summary, and more detailed information
is given in Chapters 15 and 16.
1.1 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 vapor pressure. A more informative measure of
volatility is the true vapor pressure but unfortunately this is not easily measured. It is
referred to 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 bum 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 this concentration, using a specific measuring
technique, reaches the lower flammable limit is known as the flashpoint of the liquid.
1.2 FLAMMABILITY CLASSIFICATION
There are many classification systems for defining the flammability characteristics of
petroleum liquids, most of which are based on flashpoint and Reid vapors 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 of non-volatile and volatile, as defined below, is in general sufficient to
ensure that proper precautions can be specified.
Non-Volatile
Flashpaint of 60'C or above as determined by the closed cup method of
testing.
Volatile
Flashpoint below 60"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'C, it should be treated
as volatile petroleum. Owing to their particular characteristics, residual fuel oils
should always be treated as volatile (see Chapter 24).
1.3 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 vapor 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 Chapter 15.
1.4 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 sulphide.
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 Chapter 16.
