Hi

We are looking to replace 50+ fire door closures on residential front doors in an apartment block. As long as the installer follows the manufacturer's fitting instructions, is there a requirement for the installer to have any accredited competency training and standard, or can any regular skilled trades do it?

Thanks   

The person / contractor should be able to demonstrate sufficient competence to be able to complete the job.  Make sure they have the necessary SKEB, see https://www.citb.co.uk/standards-and-delivering-training/training-standards/competence-frameworks/

If you are unsure you could appoint an independant inspector to sign-off the work https://afdi.org.uk/