How to choose a retention bund ?


Protect your environment with a retention bund

The simple retention bund are nonetheless essential equipment for the industry. They play a crucial role in the prevention of human and environmental risks. By containing various liquids, stationary or in motion, they protect professionals and the environment. They also make it possible to strictly comply with the water law.

The choice of a retention bund is made according to the use of it. This determines the materials that are used for its construction as well as its type of structure. Each type of retention bund has advantages as well as disadvantages. The compatibility between the material used for the bund and the liquid retained must be respected.

The retention bund, an industrial liquid containment system

Many industrial processes involve the use of more or less toxic or even dangerous liquids. The retention bund serves as an artificial barrier which avoids any contact with the natural environment. It has the capacity to retain different types of fluids for a more or less long duration. Liquids are stored more or less temporarily. They are pumped and then transported to a storage or final treatment area.

You can use the retention bund as a preventive safety system. It then serves to prevent any leakage of dangerous liquid both for humans and for their environment. This is particularly the case for the retention bund which equip electric transformers. These contain a polluting liquid: dielectric oil which must not spill.

Stationary or mobile use

The retention bund can be a fixed or flexible structure which allows its movement. Independently of the configuration, the security standards are just as important.

In the case of electrical transformers, the standards NF C13-200 and NF C13-100 regulate in particular the aspects of environmental protection including the retention of the dielectric. The long-term effects of dispersing certain liquids can be catastrophic. This is why the quality of the retention bund is essential to guarantee total containment.

The manufacturing as the installation of the retention bunds cannot present any defects. Compliance with applicable regulations is essential to validating your retention solution. In the event of an incident, access to specific insurance is guaranteed. It demonstrates your respect for the law. By bringing yourself into compliance, you also strengthen your company’s reputation among your customers.

Any installation concerned must comply with the water law

Each retention bund installation is subjected to a so-called “Water Law” declaration. It applies to all human activities that can affect the quality of water. This legislation is motivated by the marked deterioration in the quality of water throughout France.

The basic legislation is the same for all regions. It is however reinforced in some fragile areas. More populated, the impact of industrial activities on aquatic environments is even more closely monitored.

A declarations at the prefecture

The “Water Law” requires a declaration procedure which takes place in four main stages:

Your file must be submitted in triplicate in electronic form. Deposit the documentation at the IOTA counter where your facility depends.

Within 15 days you will receive a deposit receipt. You may have to provide certain additional or missing documents.

Once you have completed the file, the Prefect has 2 months to validate your file. Any silence on his part is equivalent to de facto approval. The Prefect may nevertheless make recommendations or require additional information.

The construction of the retention bund cannot start before the end of the 2-month period. It must await the complete delivery of all the information requested. The « Water Law » takes into account several situations of possible aquatic pollution. The construction of a retention bund avoids the rejection of liquid in fresh surface water.

The special case of transformers

The use of a retention bund with a transformer is a special case. It clearly illustrates the precautions to be taken when selecting this type of equipment.

If your transformer is under voltage, choose an INFLAMMABLE metal or concrete retention bund. The retention of liquids used in energized devices poses obvious safety concerns. This use case is very demanding in terms of choice of materials and structure of the bund. It is therefore a question of guaranteeing the retention of electric oils (hydrocarbons). Indeed, this type of liquid is likely to leak from the device but also to catch fire.

The European regulation (EN 61936-1), requests to integrate a natural fire extinguishing device. The fire retention bund are thus used to extinguish the hydrocarbons collected in the retention and thus minimize the risk of fire spread.

BAFX - Modular containment bunds fitted with a fire extinguishing system
BAFX-2 retention bund with fire protection

When off-power it is less problematic

If the transformer is not under voltage, the bund can be made of metal, concrete or flexible tarpaulin. In this case it is only used for the retention of the dielectric. If it is rather a retention bund intended for the transport or intended for a storage of material « short duration » it is preferable to choose a flexible or metal container.

When selecting your retention bund, define your specifications precisely. Some non-metallic containers are modular and therefore comply with certain standardized dimensions. It is possible to have a retention bund tailored. This is also still the case for concrete retention bunds.

All these industrial devices can be fitted with accessories that guarantee optimized operation. A metal or concrete retention bund, for durable storage, can benefit from a filtration and purging system. Do not hesitate to consult a professional in order to consider all the options available. They will make your device more efficient and in compliance with the « Clean Water Law« .

BSTUB - Tubular temporary storage bunds
BSTP flexible retention bund - Storage of transformer without voltage

Advantages, disadvantages and constraints for all types of installations

By nature, the transformer under voltage have very specific retention problems. The bund are normally planned for the long term. It can be made of concrete as well as metal.

If the metallic solution is chosen it helps the modularity. The installation is also much faster. It is a preferred solution for equipment that must be deployed over a long period.

Concrete retention bunds have the advantage of being easily made tailored. They offer great resilience in the very long term. However, they may suffer from a sealing problem. Concrete pits are systematically victims of porosity. This means that a concrete retention bund must imperatively be coated with a waterproofing coating. This must be redone every 10 years. This maintenance is justified by the good level of retention of the concrete bunds and their low construction cost.

Temporary storage is less demanding

For the transformer without voltage, the requirements are lower since it is a temporary storage. However, it can last more than a year. In this case, the use of a steel retention bund is preferred.

The use of a flexible device is the best alternative for short or medium term storage. It is recommended for the removal of a transformer or for the repair of a substation for example.

When transporting a transformer equipped with a retention bund, certain rules must be observed. It is essential that the bund is higher than the conventional one. Indeed, this is the best way to avoid any risk of spillage during the movement of the assembly.

The European agreement relating to the international transport of dangerous goods by road (ADR) regulates these convoys. For most transportations not subject to ADR, it is possible to use a flexible retention bund. However, transport subject to these standards must use specific metal retention bunds.

The three functional dimensions of retention bunds

Since February 1998, the authorities as well as the industry, have been aware of the importance of adapting the retention bunds to their contents. Whatever the volume, it is essential to avoid any polluting discharge to water and soil. Retention bunds must therefore have certain capacities which could be compared to their three functional dimensions:

  1. They must be chosen according to the product stored.
  2. The retention capacity that is most suitable for storage must be precisely determined.
  3. Finally, the third dimension, and not less important, it is the compatibility. It must be possible to determine with certainty whether different products can be stored in the same retention bund. Chemical reactions must be avoided at all costs. They endanger the integrity of the retention system.

Polyethylene or galvanized steel bund?

Depending on the product to be stored, choose a polyethylene or a galvanized steel bund. Of course for very large quantities it is generally necessary to turn to a concrete bund solution.

Polyethylene bunds are not suitable for the storage of flammable products. We will rather use them for polluting and toxic products. They are also used for the storage of aggressive chemicals, for example acids.

Galvanized steel bunds are well suited for the storage of oils, paints and solvents. They are used for hydrocarbons, pollutants and even flammable products. However, they should not be used for the retention of corrosive chemicals.

BRX – Steel modular containment bunds-3
BR steel retention bund

The volume of the container depends on the volume of the content

Storage in one or more containers with a unit capacity of less than 250 litres takes place in drums, cans or jerry cans. However, everything depends on the nature of this content. They can be flammable, except lubricants, or they can be other liquids.

When it is necessary to store a content of more than 250 litres, the minimum retention is calculated precisely. For flammable liquids, except lubricants, if the capacity is less than 800 litres use 100% of the total capacity of the container. From 800 to 1600 litres, only 800 litres of this capacity will be used. If the volume is greater than 1600 litres use only 50% of the total capacity of the container.

With other types of liquids, for a volume of less than 800 litres, use 100% of the total capacity. From 800 litres to 4000 litres use only 800 litres. For a volume greater than 4000 litres use only 20% of the total capacity of the container.

In the particular case of electrical transformers, the standards impose a retention capacity of 100%.

Note that in certain countries, it is mandatory to use 110% or even 120% bund capacity.

Respect product compatibility

If you have to store different chemical liquids together, you must check their compatibility. By using the same retention bund for certain products you can expose yourself to problems. These include vapour release and changes in corrosion properties.

The decree of February 2, 1998, section 3, article 10 clearly states that: « Bunds or receptacles containing incompatible products are not associated with the same retention. » To ensure the compatibility of different retention products, consult the table of chemical incompatibilities below :

+ they can be stored together
– they cannot be stored together
o they cannot be stored together except certain cases where particular dispositions are applied

It is a matrix for verifying the possibility of storing several products. They can be flammable, oxidizing, toxic, harmful or irritating. Certain products should only be stored together if certain conditions are applied.

For any questions, contact GMT International

Address : 405, rue du Grand Gigognan – ZI Courtine – 84000 Avignon (France)
Tel: +33 (0) 4 90 85 08 64 – Fax: +33 (0) 4 90 25 61 10