There is a major misconception that a fire will be prevented by cleaning your dryer ducting. The cleaning of your dryer ducting is an important first step. Preventing a fire involves several steps that can only be considered to be a reasonable effort. The most important area is the inside of your clothes dryer and especially around your clothes dryer's element.
This is not the type of cleaning you or your dryer duct cleaner should be doing. An appliance, any of them, should only be serviced by qualified technicians. We are not talking about a person who simply claims to know how to fix an appliance but someone who is truly qualitfied. Appliances are much more complicated today than they were 20 or 30 years ago. Just like our new vehicles that need a computer to analyize them, an appliance needs a skilled trades person!
Your clothes dryer has an element that in most cases is powered by 220 volts of electricity. This is the same type of element and power that is found in your kitchen oven! In your clothes dryer this element burns red hot and lint is highly flamable.