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Field of prevention and protection against lightning

Lightning prevention

Lightning prevention

Lightning prevention

Arrêté du 19 juillet 2011

 

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Lightning impacts prevention

Lightning impacts prevention

Lightning impacts prevention

To protect your installations from the direct and indirect  effects due to lightning two concepts are possible and often complementary: prevention and protection.

Prevention uses relevant informations on the risk of occurrence of lightning to notify users concerned. The use of this kind of concept come up in terms of organization of the operation and risk reduction.

Protection is the best known way, it can avoid any direct or indirect lightning reaches equipmentor facilities to protect. It fully proves effective if all the entry points are treated, one must speak of overall protection that can certainly circumscribe only to sensitive or critical equipment. Lightning rods, lightning arresters, for example, are employed in this case.

Cumulonimbus

Cumulonimbus

Cumulonimbus

The storm formation is either the local soil warming with creation of hot air bubbles, it is called convective storm or a cold air mass, which raises a mass of warm air loaded with moisture , we talk about storm front. Humid air heated by the sunrises and condenses into liquid droplets, thermal effects are the cloud developing the engine up.

Stormy and electrical phenomenas are come from a single type of cloud, cumulonimbus that causes heavy rains, hail, and lightning. It grows up to 3000 m until 10000 m and can contain several thousand tons of water.

The appearance of the lightning is the terminal phase of its vertical development, where a glacial process causes electrifying mechanism. Under the influence of strong vertical currents of electrical particles are created, and separate into different parts of the cloud. This separation of electrostatic charges, positive in the upper negative in the lower part, will be the engine of lightning.

Facing the negative charges of the cloud, a soil occurs influx of positive charges from a continuous current between the atmosphere and the earth. A significant electrostatic field is thus moved in the cloud.

The electrical charge having considerably increased, intra-cloud lightning results appear breakdowns between oppositely charged pockets.

Tracers

Tracers

Tracers

These intra-cloud lightning can cause the initiation of go down leader comes out of the cloud. These charges coming out of the cloud base,spread globally attracted towards the ground. The tracer is divided into many branches that spread through discrete zigzagging leaps to the ground.

Each branch is a set of bonds with a length of 10 to 50 m, which move at a speed of 0.1 to 1 m / us with a stop time of 40 to 100 microseconds.

When the lowest branch of the go down leader approaches the ground, the near field then increases sharply and the neighboring peaks local ionization (corona effect) appears resulting in upward leader.

When the distance between the two markers is such that the breakdown voltage of the air exceeded a breakdown occurs, the connection between the two tracers happen.

Electric arc

Electric arc

Electric arc

The contact between the cloud and the ground is then established, an intense wave of positive charges (those present in the cloud) pull up. These charges are the most mobile of all (earth-cloud) diffuse on surface to arrive at the point of impact.

A strong current is established in the channel created by the meeting of the two tracers. It only takes few microseconds, the time to discharge the loads involved.

It creates on its vertical travel, with a length of 3000 m on average, a strong electromagnetic field. It carries the channel to 30,000 ° C, causing a high light intensity "lightning," and a violent pressure air creating a shock wave "thunder".

Lightning is an arched back initialized by a precursor phenomenon that impacts the ground at accidents or relief on high structures.

Fillers recover under the cloud, if the ionization channel is still present, subsequent lightning strokes can still be established.

Electrostatic fields

Electrostatic fields

Electrostatic fields

The development of a storm cell causes on the ground a variation of the electrostatic field. The field on the ground is influenced by this phenomenon to a distance of approximately 10 to 30 km.

Representative effects are:

a beautiful time field 150 V/m to 400 V/m, created by the positive charges that migrate through the atmosphere to the ground,

field reversal to the birth of the storm cell,

strong growth of the electrostatic field on the ground.

From 2 kV/m, We can say that there is in the presence of storm activity. From 7 kV/m the danger is great to have lightning strikes to the ground.

On this variation can be added to electric field changes due to lightning strikes and the different distributions of the charges in the cloud.A rapid field reversal corresponds to the rise in the return stroke of lightning, positive charges from the ground to the cloud. It is characteristic of a lightning strike in close proximity.

Detection technologies

Detection technologies

Detection technologies

Measuring the electrostatic field on the ground may detect the presence of emergence of a thunderstorm cell, before any phenomenon of lightning. This is detectors storms electrostatic principle, kind mill type.

These detectors are particularly adjust to the prevention.

See the website : www.prevention-foudre.fr

Electromagnetic sensors detect the electromagnetic field radiated by ground/cloud lightning or intra cloud lightning. They can not fully respond to the need of prevention. Networked, they can allow to follow the storm fronts approach phases and trigger area on weather alerts. But they remain blind to the first lightnings.

Prevention of classified industrial estates

Prevention of classified industrial estates

Prevention of classified industrial estates

The industrial risk is one of concerns of the Ministry of Ecology and Sustainable Development. It had the desire to improve prevention through the application of Directive 82/501 / EEC called Seveso and the decree of 4 October 2010 on "the prevention of accidental risks within classified facilities for the protection of the environment subject to authorization ".

There are included, by decree of 19 July 2011, an article on the protection against lightning. This decree repeals that of 15 January 2008. However the circular of the latter, the April 24, 2008, is still usable.

It notes:"In addition to protection systems, means of prevention such as thunderstorm detection equipment or thunderstorm activity to alert service can be defined.

Prevention means are integrated into the operation of the installation procedures. "

Lightning Prevention is recognized as the lightning protection to be effective in a study lightning prevention solution will be fully accepted. Reducing the risk it brings can be considered.

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