Page 10 - Handbook of Hazardous Chemical Properties

Latent Heat of Vaporization - Defined as the heat that must be added to the specified weight of a
liquid before it can change to vapor (gas). The value varies with temperature. The value given in the
handbook is that derived at the chemical's bailing point at 1 am.. Three sets of units are given: Btu
per pound, calories per gram, and joules per kilogram. No value is given for chemicals with very high
boiling points at 1 atm, because such chemical substances are considered essentially nonvolatile.

Molecular Weight - Defined as the weight of a molecule of the chemical relative to a value of 12 for
one atom of carbon. The molecular weight is useful in converting from molecular units to weight Units,
and in calculating the pressure, volume and temperature relationships of gaseous substances. The ratio
of the densities of any two gases is approximately equal to the ratio of their molecular weights. The
molecular weights of mixtures can be calculated if both the identity and quantity of each component of
the mixture are known. Because the composition of mixtures described in this handbook are not known,
or because they vary from chemical suppliers, no molecular weights are given for mixtures.

Short Term Exposure Limits - Defined as the parts of vapor (gas) per million parts of contaminated
air by volume at 25 "C (77 "F) and atmospheric pressure. The limits are given in milligrams per cubic
meter for chemicals that can form a fie mist or dust. The values are the maximum permissible average
exposures for the time periods specified. The term Short Term Exposure Limit, or STEL, is also used
and is considered interchangeable with Short Term Inhalation Limit. The STEL designation is derived
from the OSHA standards.
Synonyms - These are alternative systematic chemical names and commonly used trivial names for
chemicals. An index of synonyms is provided at the end of the handbook to assist the reader in
researching chemical hazards information.

Toxicity by Ingestion - The designation LD,, is commonly used in the handbook. The LD, values are
those defined in most cases by the national Academy of Sciences, but actual data were collected from
various sources such as company specific material safety data sheets. The term LD, (meaning lethal
dose at the 50tb percentile population) indicates that about 50 percent of the test animals given a
specified dose by mouth will die. Thus, for a chemical whose LD, is below 50 mgkg, the toxic dose
for 50 96 of animals weighing 70 lb (150 kg) is 70 x 50 = 3500 mg = 3.5 g, which is less than one
teaspoon. For a chemical with an LD, value of between 5 to 15 g/kg, the amount would be between
a pint and a quart for a 150 lb man.

Threshold Limit Value - The term refers to toxicity by inhalation. The abbreviation used is TLV. The
TLV is usually expressed in units of parts per million (ppm) - i.e., the parts of vapor (gas) per million
parts of contaminated air by volume at 25 "C (77°F) and atmospheric pressure. For chemicals that form
a fine mist or dust, the concentration is given in milligrams per cubic meter (mg/m3). The TLV is
defined as the concentration of the chemical in air that can be breathed for five coIlsecutive eight-hour
workdays (i.e., 40 hours per week) by most people without suffering adverse health effects. This is the
definition given by the American Conference of Governmental Industrial Hygienists.

Vapor (Gas) Specific Gravity - Defined as the ration of the weight of the vapor to an equal volume
of dry air at the same conditions of temperature and pressure. Buoyant vapors have a vapor specific
gravity less than one. The value may be approximated by the ratio W29, where M is the molecular
weight of the chemical and 29 is the molecular weight of air. In some instances, the vapor may be at
a temperature that is different from that of the surrounding air. For example, the vapor form a
container of boiling methane at -172 "F sinks in warm air, enough though the vapor specific gravity of
methane at 60 "F is about 0.6.

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