I have just completed a new kitchen and garage. The kitchen is just being fitted with a cooker hood over. I cannot vent straight to an outside wall so plan to use the 150mm flat ducting to take it through the garage. I am told by the planning department that I have to use a special type of ducting which includes a fire check. The idea apparently is to stop the spread of fire from one room to another. 
Does anyone know what it is called or where I can look for it?
Any help would be much appreciated.
