To the best of my knowledge, no accreditations/ qualifications are required. However, personally, I don't use any company that isn't accredited to BAFE scheme SP201, or SP203 part 1. If it included a gas drenching system, I'd look for additional accreditation to BAFE scheme SP203 part 3. There are other accreditations about, but in my experience BAFE is one of the more robust in terms of auditing.