This video aims to give you a 10 minute long introduction on what bunds are and a guide to their design, construction, maintenance and repair. This video covers industry standards for bunds in the United Kingdom but cannot be applied to all sites; COMAH sites for example will require extra considerations which may not be covered by the contents of this video.
The first area of bund design we will look at is capacity. The industry standards are the 110% and 25% rules. These rules can cause some confusion so they are explained.
Bunds are generally designed to have as small a footprint as possible however there are other factors you need to consider.
As a minimum you should have a 750mm separation distance between the tank and the bund walls.
Walls should be constructed no taller than 1.5 meters wherever possible. To help combat the tidal wave effect you can install additional infrastructure to the bunds which limit the amount of liquid which could overtop the bund in the event of a catastrophic failure.
Bunds can be constructed from reinforced concrete or reinforced masonry; however sites may have specific requirements related to construction materials which will need to be adhered to.
Consideration could be given to prefabricated bund walls, these systems are typically cheaper and quicker to install than traditional bund walls and can be dismantled are reassembled if necessary.
In all instances bunds must be designed and constructed to withstand the pressure exerted on them by a catastrophic tank failure this can be up to 6 times the hydrostatic pressure.
Following a new bund install hydrostatic testing should be conducted to ensure the bund is watertight before the bund is put into use.
Wherever possible pipes and cables should be run over bund walls and not through the bund walls or floor. If penetrations are unavoidable it is essential to ensure they have a watertight seal installed around the pipe/cable, the sealant material must be resistant to the product stored in the bund.
In order to make a bund impermeable a specialist lining can be applied to the bund walls and floor which provides an effective seal ensuring the bund is watertight; different lining materials are available but they should be designed to withstand attack from the material stored inside the bund.
In order to prevent rainwater entering a bund and reducing its capacity it is preferable to install a roof above the bund, however this is often not an option. Where it is not possible to cover a bund it is imperative an appropriate maintenance regime is in place.
Rainwater and other debris should be removed regularly. Whenever removing substances from a bund it is essential to test for contamination before they are disposed of. If they are contaminated they will need to be disposed of in line with waste regulations or pumped to a suitable control measure such as an effluent tank or interceptor. Contamination levels can be very low and still require treating as hazardous waste, for oils the threshold can be as little as 0.1%.
For oil bunds automatic bund dewatering units can be installed. The systems discriminate between oil and water to within 5 parts per million and pumps out only the water leaving the oil behind.
As well as conducting regular rainwater removal periodic checks should be undertaken assessing the condition of the bund walls, floor, any penetration seals and bund linings. If any defects are recorded they should be repaired as quickly as possible to prevent the problems from becoming worse. In addition to visual inspections hydrostatic testing can be undertaken to test if a bund is watertight, the bund is filled with water with any loss of liquid recorded by specialist equipment over a set period of time.
If bunds have developed cracks they will need to be repaired to ensure the bund is not only watertight but retains the structural integrity to withstand a catastrophic failure.
If the bund lining has failed the bund will need relining or patch repairs to be undertaken.
We hope you found it useful and if you require any assistance with your bunds please get in touch on 01656 741 799 or sales@GPTenvironmental.co.uk.
30 июл 2024
