Stopford have featured again in this quarter’s Tank Storage Association newsletter issued today. This went out to 22 companies operating ~300 terminals in the UK and ROI. Stopford’s article focused on CIRIA C736 guidance.
Protecting our Planet, are your Pollution Prevention controls adequate?
The CIRIA C736 guidance was developed to assist owners and operators of industrial and commercial facilities storing substances (inventories) that may be hazardous to the environment.
This article highlights key areas from the CIRIA guidance for TSA members to consider.
The original CIRIA R164 Design of containment systems for the prevention of water pollution from industrial incidents 1997 was written primarily for new construction with many of the principles applied to good effect on existing sites. This has been revised and updated to reflect changes in legislation, construction design and practice and lessons learned from recent incidents, particularly, Buncefield.
Current Industry Practice
The basis for much industry practice in the past has been the 110% and 25% rule where a single tank is bunded, the recommended minimum capacity is 110% and where two or more s are installed in the same bund, the recommended capacity is the greater of:
- 110% of the largest tank
- 25% of the capacity of all the tanks
The 10% margin has been interpreted by industry and regulators to cover a range of factors including:
- Prevention of overtopping
- Allowance for firefighting agents
- Protection against overfilling
- Allowance for rain
and the 25% rule assumes that it is unlikely for more than one tank to fail at any one time.
Assessment of containment capacity
Based on the principle that the containment should be capable of retaining:
- Volume of inventory released during a credible incident
- Maximum rainfall likely to accumulate before, during and/or aster an incident
- Firefighting agents including cooling water
Volume of inventory
The brimful capacity of the primary containment should normally be adopted, if a physical overflow is fitted, the capacity up to the overflow may be taken.
In some cases, the nominal or tank rated capacity may be used, subject to a risk assessment and agreement with regulators.
In the UK, the allowance for accumulated rainfall should be based on a 1 in 10-year return period (annual exceedance probability of 10%) event.
An allowance in the height of the wall (freeboard) should be agreed with the Fire and Rescue Service, but no less than 100mm.
Normally, it would be impractical to design a secondary containment for firefighting and cooling water from a major fire. The Fire and Rescue Service should be consulted and one of the following options agreed:
- Procedure for recycling cooling water to ensure no build up in the bund
- Maximum amount of cooling water required in the worst-case scenario
Some inventories, such as fatty acid methyl esters and ethanol, dissolve and emulsify in water and may not be suitable for recycling.
Option 2 is likely to require local secondary containment well in excess of the volume of inventory which will translate into high bund walls.
Stopford have carried out several containment/bund design studies balancing the conflicting requirements of increased secondary containment against practicable bund heights and available areas.
Find our contact details on the TSA website here.