Can Plastic/UPVC and PP Ductwork be used for connection to Dust Extraction systems?
No, plastic ducting is not usually suitable for movement of particles (i.e. dust /shavings) as these may require a higher velocity than the duct is designed for and may pose ignition, fire and explosion risks. BS EN 12779:2004 and HSE WWIS 32 require that ductwork for wood dust should be conductive e.g. steel, because wood dust is potentially explosive and there is a risk of a static ignition source with non conductive ducting.
There are four main reasons why it is not suitable, these are:
(1) Risk of Static generated sparks igniting a dust explosion
The 2 types of “Plastic” ductwork, UPVC & PP, generate static which can spark and ignite the dust. Examples of dusts that are flammable and/or potentially explosive: most fine dust particles including wood, flour, sugar, animal feed, pharmaceuticals, chemicals & metals. Explosive atmospheres legislation therefore requires that ductwork must be manufactured from a conductive material, i.e. Steel, so that any static electricity generated can be discharged to earth.
(2) Plastic Ductwork is usually designed for low velocities
Principles of system design specify that the minimum air velocity necessary to keep dust and chippings airborne is 10 to 25 m/sec. UPVC and PP ducting is designed to be used with a system where the air velocity is less than 10 m/sec. It is therefore unsuitable to use UPVC and PP because the velocity is too low and the waste will settle out of the air stream through the ductwork, causing blockages and increasing the risk of dust explosion. Plastic ducting may leak dust when used at the high velocities necessary to keep the dust airborne within the ductwork.
(3) Abrasion Damage
Many dusts are very abrasive and will damage the plastic duct causing leaks. You must check the manufacturer’s specification for suitability for use with, and resistance to abrasion by, the dust concerned.
(4) Duct Design Restrictions
Duct designs for dust extraction must have swept wide throat 90 degree bends, 30 degree angle branch entry and Y piece duct connections to minimise resistance to airflow. Ordinary 90 degree bends and Tee pieces should never be used as the dust will settle out of the airstream, causing duct blockages.
UPVC and PP technical information:
Electrical Classification - an insulator.
The surface resistivity of both UPVC and PP is greater than 1014 ohms and electrostatic charge cantherefore accumulate easily.
UPVC: Burns when in contact with a flame, giving off black smoke. Stops burning on extinction of the flame, and evolves white fumes for a time. The products of combustion are noxious.
PP: Ignites readily and melts and drips as it burns. Gives off black smoke on burning, the quantity depending on the fire conditions.
YOU MUST CHECK THE MANUFACTURER’S SPECIFICATION FOR:
RECOMMENDED MAXIMUM AIRFLOW VELOCITY
STATIC DISCHARGE PROPERTIES
COMBUSTIBILITY & BURNING CHARACTERISTICS