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In all seriousness, I'm sure it was perfectly safe and they were just being careful. Although he did say the normal operating speed when it was in place in its factory in Manchester was 18 rpm and it was going a hell of a lot faster than that!
Well worth a visit when in Norfolk: http://www.forncettsteammuseum.co.uk has one of the Tower Bridge engines which is most cool
(P) what's this?