Chemical Tankers / Day 2 / Day 2 Topic 1 USCG Chemical Guide

1.5 Explanation of physical properties of cargo

o Freezing Point

The temperature in “C” and in “F” at which the liquid solidifies.

Important information for carriage and discharge temperatures and for method of cleaning.

1.5 Explanation of physical properties of cargo

Physical Properties & Regulatory Classification

1.5 Explanation of physical properties of cargo

o Vapor Pressure

The pressure exerted by the vapor above the liquid. Measured in millimeters of Mercury (760 mm Hg = 14.7 psi) at 20C.

psi = mm Hg / 760 x 14.7

1.5 Explanation of physical properties of cargo

o Reid Vapor Pressure

The vapor pressure of a liquid determined by laboratory testing in a standard manner in Reid Apparatus at standard temperature of 100F (37.8C) and expressed as pounds per square inch absolute (psi).

1.5 Explanation of physical properties of cargo

o Vapor Density

This is actually a specific gravity as it equals the ratio of the weight of vapor or gas compared to the weight of an equal volume of air at the same temperature and pressure.

1.5 Explanation of physical properties of cargo

o Vapor Density cont.

Values less than 1 indicate that the vapor tends to rise and value greater than 1 indicate that it tends to settle.

1.5 Explanation of physical properties of cargo

o Vapor Density cont.

Values less than 1 indicate that the vapor tends to rise and value greater than 1 indicate that it tends to settle.

Useful when considering a dangerous build up of gases on deck during cargo or tank ventilation operations.

1.5 Explanation of physical properties of cargo

o Solubility in Water

The following terms are used to describe the solubility of the product by weight in cold water:

Negligible - less than 0.1%

Slight - 0.1%-1%

Moderate - 1%-10%

1.5 Explanation of physical properties of cargo

o Solubility in Water cont.

The % by weight will be given when solubility is of particular importance. For example, a highly toxic material which is only slightly soluble.

1.5 Explanation of physical properties of cargo

o Solubility in Water cont.

Useful information for safety and tank cleaning purposes:

-if product is insoluble, water may not be an efficient fire fighting medium;

-if product insoluble, traces of toxic cargoes may be contained in the sump residues of the tanks. More time should be spent for cargo cleaning;