ATEX and explosion protection

What is explosion protection and when is it required? When must test systems be designed in accordance with ATEX directives? These are just some of the questions asked by our customers.

ATEX, explosion protection for climate chamber

Explosive atmospheres can be caused by flammable gases, mists or vapors or by combustible dusts. If there is enough of the substance mixed with air, then all it needs is a source of ignition to cause an explosion.

In general, flammable mixtures are

  • Gas / air mixtures
  • Aerosol / mist / air mixtures
  • Dust / air mixtures

Explosions can cause loss of life and serious injuries as well as significant damage. Preventing the creation of explosive atmosphere or preventing sources of ignition are two widely used ways of reducing the risk.

The formation of these mixtures can be initiated by a fault in the system. The fault may be unwanted or rather deliberate, by a constituent of a test.

A mixture is explosive if the concentration is within certain substance-specific limits. These limits are designated as lower explosion limit (LEL) and upper explosion limit (UEL) and are indicated in our material data sheet.

A fire or explosion hazard requires protective measures taken at the chamber and/or installation site, dependent upon the danger level.

The Vötsch test systems are equipped with relevant devices that represent potential sources of ignition e.g. heaters and lighting, which increase the risk of an explosion.

Weiss test chambers can be modified, upgraded and installed with the relevant safety devices to ensure compliance with ATEX directives.

What is ATEX?

ATEX (derived from the French term "ATmosphères EXplosibles) is the name commonly given to the two European directives for controlling an explosive atmosphere - 99/92/EG and 94/9/EG.

Since 1st July 1st 2003, these directives are legally binding. The installation of explosion-proof systems that do not comply with these directives will no longer be permitted.

Directive 99/92/EG describes the duties of the system user whereas directive 94/9/EG lays down the duties of the system manufacturer.

The primary duty of the system user is the assessment of potential danger in addition to the classification of potential danger within the system - so-called ‘zones’.

The system manufacturer must carry out the classification and labelling of the systems according to the risk of igniting potentially explosive mixtures - so-called system ‘categories.’ This duty links the system manufacturer with the system user.


1. Undertake a danger assessment 
The user must undertake a supervised danger assessment of the test systems, in addition to the working appliances. The zones of explosion-sensitive areas in the systems must be determined. The identification of all existing materials as well as possible electrical and non-electrical ignition sources and their assessment with regard to the risk of explosion, is of paramount importance.

Classification into zones 
The assignment of the explosion-sensitive areas into zones is for the fixing and determination of the safety requirement and protection systems for the chambers. The respective zone/s determine the category in accordance with which the chambers and components have to be designed and tested.

2. Compile documentation for explosion protection 
In accordance with the individual dangers, the system user or the system manufacturer has to implement suitable explosion safety measures.

A plan must be drawn up for safety measures for the used electronic and non-electronic accessories and detailed in the prescribed explosion safety document.

Zone 0 
Area in which the presence of an explosive atmosphere as a mixture of flammable substances in the form of gas, steam or mist with air, is permanent, long-term or frequent. 
Zone 1 
Area in which explosive atmosphere as a mixture of flammable substances in the form of gas, steam or mist with air during normal operation is expected occasionally. 
Zone 2 
Area in which during normal operation an explosive atmosphere as a mixture of flammable substances in the form of gas, steam or mist with air is not expected. However, if it still occurs then for a short period of time, only.


We take our responsibilities as an environmental equipment manufacturer very seriously. The continued success of our ATEX projects is primarily due to close cooperation with our customers - detailed knowledge regarding planned tests, applications and application use are crucial for the optimum design and development of our test systems.

In accordance with guideline 94/9/EG, our temperature and climatic test cabinets fall into system group II.
This group is divided into 3 categories:

Category 1 
Category 1 comprises test systems designed to be operated in accordance with the characteristic values specified by the manufacturer and guarantee a very high degree of safety.

Systems of this category must guarantee the relevant degree of safety even during rarely occurring system failures. They must therefore, contain explosion safety precautions. In the event of a technical safety precaution failure, at least a second independent technical safety precaution guarantees the required safety. The required safety is even guaranteed if two independent faults should occur.

Category 2 
Category 2 comprises systems designed to be operated in accordance with the characteristic values specified by the manufacturer and guarantee a high degree of safety.

The technical explosion safety measures of this category guarantee the required degree of safety during frequent system failures or errors which are usually to be expected.

Category 3 
The third category comprises systems which are designed to be operated in accordance with the characteristic values specified by the manufacturer and guarantee a normal degree of safety.

Systems of this category are designed for use in areas where an explosive atmosphere via gases, steam, mist or raised dust is not expected. Should it be become present, it is for a temporary and short period only.

Customized solutions

The safety devices applied for each project are guaranteed to meet the customer’s specific requirements. This is achieved thanks to a modular system that combines one or several more safety measures in one unit.

Should you require further information, please refer to guidelines or contact us for expert advice.


Top priority of the explosion protection is the primary explosion protection.

The secondary explosion protection is only applied if sufficient safety cannot be guaranteed by the primary explosion protection or if the primary explosion protection cannot be applied.

The tertiary explosion protection is only applied if both the primary and the secondary explosion protection cannot be applied demonstrably.