# The Control of Major Accident Hazards Regulations 1999, Paragraph 4


The addition of dangerous substances to determine the quantity present at an establishment shall be carried out according to the following rule:—
if the sum
q1Q+q2Q+q3Q+q4Q+q5Q+...>1 where
qx the quantity of dangerous substances x (or category of dangerous substances) falling within Parts 2 or 3 of this Schedule,
Q the relevant threshold quantity from Parts 2 or 3,
then the establishment is covered by the relevant requirements of these Regulations.
This rule will apply for the following circumstances—
(a) for substances and preparations appearing in Part 2 at quantities less than their individual qualifying quantity present with substances having the same classification from Part 3, and the addition of substances and preparations with the same classification from Part 3;
(b) for the addition of categories 1, 2 and 9 present at an establishment together;
(c) for the addition of categories 3, 4, 5, 6, 7a, 7b and 8, present at an establishment together.

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Source: https://www.legislation.gov.uk/uksi/1999/743/schedule/1/part/5/paragraph/4 (the official version)
Page: https://openlegislation.uk/control-of-major-accident-hazards-regulations-1999/schedule-1/part-5/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.