HSE-relevant Properties of Chemical Substances

The hazardous nature of all chemicals is strongly grounded in their physico-chemical properties, the magnitude of which determine the degree (or intensity) of the hazard posed by them. Table 1 provides a list of such common properties of substances, which often are indicative of the level of hazard and which constitute inputs to quantitative (or semi-quantitative) assessment of hazard posed by a chemical [Refs. 3, 4,5].

Table 1. Physico-chemical Properties defining Hazards

Appearance :

 - indicate physical state (solid, liquid, gas), and colour


 - if odour is perceptible, give a brief description



Boiling point/boiling range:

 - specify here the temperature at which the material changes from liquid to gas. If it decomposes without boiling, the temperature at which it decomposes may be given with the abbreviation `dec.'

Melting point/melting range:

 - indicate the temperature at which the solid material changes to a liquid

Flash point:

 - the lowest temperature at which a liquid or solid produces enough vapour to form a flammable air-vapour mixture near its surface so that it can be ignited by a spark or flame at atmospheric pressure.


 - to provide an indication of acidic or alkaline (basic) properties, give the pH of the substance or preparation as supplied or that of an aqueous solution (in the latter case indicate the concentration).

pH is expressed on a scale from 0 to 14, which can be divided into the following ranges: 

  • pH 0-2 Strongly acidic 
  • pH 3-5 Weakly acidic 
  • pH 6-8 Neutral 
  • pH 9-10 Weakly basic 
  • pH 12-14 Strongly basic 

Substances or preparations with pH values 0-2 or 11.5-14 may be classified as corrosive.


 - describes the ability of the material to ignite and burn readily. A liquid or solid with a flash point above 21°C but less than 55°C is flammable.

Highly flammable relates to substances or preparations with a flash point above 0°C but below 21°C, as well as to solids spontaneously flammable in air or which may readily ignite after brief contact with source of ignition and which continue to burn after removal of the source of ignition.

Extremely flammable relates to liquids which have a flash point below 0°C and a boiling point below 35°C, and to flammable gases when liquefied.


- some materials have the feature of igniting in air in the absence of a spark or flame. The auto-ignition temperature can be found in the literature.

Explosive properties:

 - specify, if appropriate, the concentrations for the lower and upper explosion limits. This is usually in volume percentage of air, for example, for xylene 1.1-7.0%, and for benzene 1.2 - 8.0%.

Oxidizing properties:

 - substances which can generate and maintain heat producing chemical reaction with other materials, especially burning flammable material.

Vapour pressure:

 - describes the tendency of a material to form a vapour. It is used e.g. for estimating the inhalation or fire hazards. Vapour pressure is expressed usually at the temperature of 20°C.

Relative density:

 - the density of the substance or preparation compared to the density of water (= 1). This figure indicates whether the substance floats in water or sinks (when the relative density is more than 1).


 - indicate here the solubility in water. If the solubility is not accurately known describe with words such as: poor, moderate, miscible...

Partition coefficient:

 - the ratio of the solubility of a substance or preparation in n-octanol to that in water.

Other data

 - provide here data relevant for safety aspects, such as vapour density, evaporation rate, conductivity, viscosity, etc.


 - abbreviation used for the dose which kills 50% of the test population. LD50 is expressed in milligrams per kilogram of body weight of the test animal (which must be mentioned).


 - abbreviation used for the exposure concentration of a toxic substance lethal to half of the test animals. LC50 is expressed in millilitres per kilogram of body weight of the test animal (which must be mentioned), exposed to the substance by inhalation during a specified period.

TLV-TWA (Threshold Limit Value - Time Weighted Average)

 - time-weighted average concentration for an eight hour working day or 40 hours a week to which nearly all personnel may be repeatedly exposed without adverse effect. 

TLV-STEL (Threshold Limit Value - Short Term Exposure Limit)

 - concentration to which a person may be exposed for a short time (usually 15 minutes) without suffering from irritation, long-term or irreversible tissue damage or impairment likely to increase accidental injury, affect self-rescue or reduce work efficiency

TLV-C (Threshold Limit Value - Ceiling)

 - concentration that should not be exceeded at all during work exposure