A table encompassing Permeation Index Numbers utilizing both breakthrough times and permeation rates was first proposed by Krister Forsberg at the First International ASTM Symposium on the Performance of Protective Clothing, 16-20 July, 1984 in Raleigh, North Carolina and published in, "Performance of Protective Clothing," (ASTM STP 900, p. 247, 1986) ASTM, Philadelphia, PA.
The following Index Numbers are an extension of this philosophy which covers all possible combinations of breakthrough time and permeation rate.
Division of chemicals versus protective materials into the classifications below is a logical and conservative progression. The chemical permeation Index Numbers provide a useful guide to help in selection of the best protective materials when there is more than one choice available or to provide some relative risk assessment if data is available for only one type of material. Final selection should also include degradation data when it is available.
Index 0 and Index 1 apply to the most resistant materials towards a specific chemical or test mixture. Index 0 is the best and most resistant material and is recommended.
Index 1 indicates a highly resistant material and may often be accepted by an industrial hygienist for harmful chemicals (e.g., as toxic as toluene or as corrosive as concentrated sodium hydroxide or as irritating as acetaldehyde).
Index 2 requires a greater degree of judgment by an industrial hygienist before it will be accepted. Industrial hygienists will not feel comfortable in recommending Index 2 materials for chemicals that are harmful (where a relatively small dose has a medium to moderate toxicity).
Index 3 materials are not usually sufficiently protective to be recommended by industrial hygienists unless there is no other choice or unless the work involves protection only against occasional splashes or compounds that are not very harmful.
Index 4 materials are usually not acceptable for protection in any situation except occasional splashes. When splashes occur with materials in either Index 3 or 4 the gloves, or other types of protective clothing, should be immediately removed and exchanged for new ones.
Index 5 materials may be considered dangerous by most industrial hygienists because of the lack of protection they offer towards the chemical(s) tested.
Clothing material test results with classification Index Numbers of 4 or 5 may exhibit one or more forms of degradation. It is important to note that a material which has an Index Number of 4 or 5 against one particular chemical may in fact be rated with an Index Number of 0 or 1 against some other chemical. Therefore, these Index Numbers are not to be construed as a rating of a protective material except in the case of its use for protection against the specific chemical referenced and under the conditions of the measurements.