In short: wherever environmental pollution (= leakage of liquids hazardous to water) must be reliably prevented.

Requirement from the water law regulations (Germany)

The AwSV defines the basic requirements in § 17. They apply nationwide. The necessity of using leak detectors is based on §18, sentences 1 to 3:

(1) Facilities must retain leaked substances hazardous to water in a suitable manner. For this purpose, they must be equipped with a retention device as defined in § 2, paragraph 16. Sentence 2 does not apply if it is a double-walled plant within the meaning of § 2 paragraph 17 ...
And with §2, para. 17:

(17) "Double-walled systems" are systems consisting of two independent walls, the interstitial space of which is designed as an interstitial space equipped with a leak detection system indicating leakage from the inner and outer walls.

A leak detection system (consisting of a leak detector, connecting lines and interstitial space) prevents the leakage of water-polluting substances/liquids.

To achieve this goal, both walls (primary and secondary wall) are constantly monitored - both above and below the liquid level.

A leak in one of the two walls triggers the leak detector alarm and that before water-polluting products can get into the environment.

This means that leak detectors differ significantly from sensor leak detection systems. The latter can "only" determine the occurrence of liquid, without making any statement about the condition of the secondary barrier.

The use of a leak detector requires a double-walled system. The space between the two walls is the interstitial space.

Some examples of double-walled systems:

- Double-walled tanks made of steel or plastic or combinations thereof
- Single-walled tanks with a rigid or flexible leak protection lining
- Double bottoms of flat bottom tanks
- Double-walled pipelines (steel/plastic/combination)
- Surface seals made of foil (e.g. under concrete surfaces)

Currently, the standard EN 13160 "Leak detection systems" with the corresponding parts is included in the MVV TB. There it is regulated that the leak detectors either bear the Ü mark or directly the CE mark. The latter applies to systems for heating or cooling.

The previously known abZ (general technical approval) is thus obsolete.

Note: The aforementioned standard falls under the Construction Products Regulation. The water law requirements are regulated by the WasBauPVO.

Tanks/containments
Pressure leak detectors create an overpressure in the interstitial space of the double-walled tank that is higher than the pressure of the stored liquid (or groundwater) against the interstitial space.

If a leak occurs, air bubbles through this leakage either into the inner tank or into the ground. Due to the escaping air, the pressure in the interstitial space drops and the alarm is triggered. The pressure conditions are designed in such a way that no product can enter the interstitial space even if an alarm is given. The compressed air creates a kind of "protective shield" around the stored product.

Pipes/Pipelines
For pipelines, pressure leak detectors are also often used with nitrogen instead of air. The function is as previously described, but the alarm pressures are significantly higher than the delivery pressure in the inner pipe and are therefore significantly higher than with tank monitoring.

Vacuum leak detectors (also called negative pressure leak detectors) generate a negative pressure in the interstitial space. In the event of a leak, all media adjacent to the interstitial space are thus sucked into the interstitial space and no product can escape into the environment.

In case of an air leak (outside or inside above the liquid), air is sucked into the system. The pressure change causes an alarm (as with the overpressure leak detectors, except that air is sucked in).

Tank/Vessel
In the event of a liquid leak, the stored product (or groundwater) is sucked into the interstitial space. This fills up until it reaches the liquid barrier in the leak detector suction line and closes it. With the closing of the liquid barrier, the pump built into the leak detector cannot build up any further negative pressure. Due to the negative pressure that is still present, more liquid is sucked into the interstitial space and the negative pressure is reduced to the alarm pressure. The alarm will be triggered.

Pipe/Pipeline
In the event of a liquid leak on a double-walled pipeline, liquid is also drawn into the interstitial space. This fills up, then the liquid is pumped through the manifold and node into the liquid barrier in the suction line. Due to the negative pressure still present on the measuring line side, liquid is sucked into the pressure compensation vessel and thus the negative pressure is lowered to the alarm and the alarm is triggered.

AwSV refers to the German Federal Ordinance on Installations for Handling Substances Hazardous to Water. It came into force on August 1, 2017 and replaced the previously applicable state ordinances (VAwS).

The aim of the Federal Ordinance is water protection. It includes, on the one hand, regulations on the classification of substances and mixtures according to their hazardousness. On the other hand, it regulates the technical requirements of facilities that handle substances and mixtures hazardous to water, as well as the obligations of the operators of these facilities.

(see also: www.brd.nrw.de/themen/umwelt-natur/wasser/wassergefaehrdende-stoffe-awsv/anlagen-zum-umgang-mit-wassergefaehrdenden-stoffen)