From the old now out of date guidance L73, before they improved it. So, despite the Legislation and ACOP changing, the intent for the escape of substances seemed to always include asbestos as below. However still a little vague regarding quantity in para 153.
Hope it helps
Chris
Escape of substances (paragraph 21)
150 The substances covered by this definition may be in any form: liquid, solid (eg
powder), gaseous or vapour and may include, for example:
Guide
Schedule 2, Part I
A guide to the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 Page 51 of 92
Health and Safety
Executive
(a) substances which may be hazardous to health (eg asbestos, phosgene,
toluene diisocyanate);
(b) substances which may be either corrosive or potentially hazardous by virtue of
their temperature or pressure (eg nitric acid, molten metal, liquid nitrogen);
(c) substances which may, depending upon the circumstances of the escape,
present a fire or explosion hazard (eg oxygen, acetylene).
151 Examples of the kinds of incident involving substances which might be
covered by the definition are escapes arising from the failure or breakage of plant,
pipes, equipment or apparatus; failures of process control; the operation of a relief
valve or bursting disc where the escaping substance is not safely controlled or
directed; and spillages from containers and equipment.
152 Releases from plant etc during the normal course of operation or maintenance
(eg during sampling, packaging or draining of lines) that are sufficiently well
controlled to ensure that no person is put at risk would not be reportable.
153 The decision as to whether or not an incident is reportable depends upon
factors such as the nature of the substance and its chemical, physical and
toxicological properties, the amount which escaped and its dispersal, and whether
people could have been present at the time.