3. Application

These Regulations shall not apply to —

any premises where building operations or any work of engineering construction are carried out; and

any premises where —

the number of persons at work within the premises is ordinarily less than 10 (whether or not they are all at work at those premises at the same time); and

none of the following is used or created:

any mechanical power, steam boiler, steam container, steam receiver, air receiver, refrigerating plant pressure receiver or gas plant; and

any highly flammable or noxious substance.