Heavy with facts

It is surprising that Lesley Mcleod, a representative of the Association of Project Safety (“Blaze tragedy at Grenfell Tower should ring alarm bells for all of us”, 7 July), should make the mistake of claiming that carbon monoxide (CO) is “heavier than air”.

In fact CO is slightly lighter than air and mixes well. If it is

escaping from a heating appliance it is likely to be warm and so rise through air, which is why CO detectors are recommended to be placed at a high level.

STEUART CAMPBELL Dovecot Loan, Edinburgh