Volume 1, Number 3
Oct 1994

Letters

To the Editor:

In the APA for July, 1994, you report that there is some uncertainty concerning the definition of permanence, and that this uncertainty needs to be resolved. No mention was made of durability, but the ISR program hopes eventually to be able to define both permanence and durability.

These definitions are like the definition of truth--we can seek, and perhaps get close, but quantitative definitions will never be achieved.

ASTM D 6.20 has followed the lead of ANSI IT9.1, and uses the terms Life Expectancy, and Life Expectancy Designation. The definitions are:

Life Expectancy (LE) - The length of time that information is predicted to be retrievable in a system under extended storage conditions.

LE Designation (LED) - A rating in years for the life expectancy of records.

Maximum Life Expectancy - LE-1000 - The document is expected to be usable for 1000 years.

High Life Expectancy - LE-100 - The document is expected to be usable for 100 years.

Medium Life Expectancy - LE-50 - The document is expected to be usable for 50 years.

The terms maximum, high, and medium are arbitrary, but the LE designations indicate the expected longevity in years. The greater the value of LED, the greater the uncertainty of being able to define the characteristics of a paper that can meet this life expectancy.

It is clear that one must be able to define LED in terms of a very dependable accelerated aging requirement, or in terms of composition requirements, or both.

Durability is defined by ASTM D 6.20 as follows:

"Durability is the ability of a paper to resist the effects of wear and tear in performance situations. For example, paper currency should be durable, but maximum permanence is not necessary."

Durability can only be estimated in the laboratory from data on physical and chemical tests. Laboratory data must be generated on representative papers, and the performance of these papers in the field then compared with the laboratory data.