— DT dilution tunnel (Figures 4 to 12)
The dilution tunnel:
shall be of a sufficient length to cause complete mixing of the exhaust and dilution air under turbulent flow conditions,
shall be constructed of stainless steel with:
a thickness to diameter ratio of 0.025 or less for dilution tunnels of greater than 75 mm inside diameter,
a nominal wall thickness of not less than 1.5 mm for dilution tunnels of equal to or less than 75 mm inside diameter,
shall be at least 75 mm in diameter for the fractional sampling type,
is recommended to be at least 25mm in diameter for the total sampling type.