Explosion protection in pressure sensors

Explosions can be powerful and generally cause significant damage. With this in mind, when creating electronic devices for use in explosive environments, the ultimate goal is to completely prevent explosions. KELLER AG für Druckmesstechnik has been producing products for use in explosive environments since 1988. These certified products ensure safe operation in a wide variety of applications.

Consequences of Explosions

Explosion at TotalFinaElf in Toulouse*

On September 21, 2001, 300 tons of synthetic fertilizer exploded at a plant owned by TotalFinaElf. The explosion resulted in the deaths of 22 employees and 7 local residents, with 2,500 people injured. As with previous industrial disasters, the risks were known in advance, yet the exact causes remained unclear after the incident.

Explosion at Bayer in Wuppertal*

On June 8, 1999, an explosion followed by a fire occurred at the Bayer AG plant in Wuppertal. More than 100 people were injured in this disaster, millions were paid in damages, and debris remained around the boiler house. Fortunately, no fatalities occurred, but the released chemicals and soot caused long-term respiratory difficulties, headaches, nausea, eye and skin irritation for countless people.

* Source: Bureau Veritas, former training instructor

What Causes Explosions?

An explosion is a sudden chemical reaction involving a flammable substance in the form of gas, dust, vapor, or suspension, which combines with oxygen and releases a large amount of energy. If the mixture reaches a certain concentration level, it becomes an explosive atmosphere. If the concentration is too high (rich mixture) or too low (lean mixture), a stable combustion reaction occurs without an explosion. The mixture is explosive upon ignition only if it is between the upper and lower explosive limits. The explosive atmosphere limits are influenced by ambient pressure and the oxygen content in the air.

Explosion Protection

Over a century ago, the necessity and importance of comprehensive explosion protection measures were demonstrated by numerous destructive incidents of the past. It was then that the first government regulations and laws were adopted, which remained in effect until 1994. Since 1994, explosion protection has been regulated by European Directives:

ATEX 95 or 94/9/EC (Equipment and protective systems intended for use in potentially explosive atmospheres)

ATEX 137 or 1999/92/EC (Minimum requirements to improve the safety, health, and protection of workers exposed to the risk of explosive atmospheres)

Companies operating in potentially explosive environments must implement at least two measures to prevent explosions. The primary measure involves preventing the formation of an explosive atmosphere from the outset. The concentration level can be altered and made safe by using the following measures:

• replacing flammable substances with safe alternatives.
• adding nitrogen, carbon dioxide, etc., which neutralize flammable substances.
• using natural or artificial ventilation to limit concentration.

If it is impossible to create an explosion-safe environment, then as a secondary measure, the risk potential must be divided into three hazardous zones according to the likelihood of an explosion source occurring. These three zones indicate whether an explosive atmosphere may occur continuously, periodically, or for a short time. This approach allows for the appropriate selection of devices intended for use in these zones.

Concentration range for an explosive atmosphere containing flammable substances.

Explosion-Proof Devices

Devices used in potentially explosive environments must be designed to provide the protection required for the specific hazard class. Explosion-proof devices are regulated by various directives and standards to ensure the necessary protection is always provided. Depending on the geographic location, there are different licensing authorities and sets of standards.

Explosion-proof devices for the European market undergo testing and certification according to European Directive 2014/34/EU (which replaces the original Directive 94/9/EC). All devices for this market must be developed in accordance with the EN 60079 standards. These standards cover areas at risk of gas and dust explosions and classify devices by ignition types. They define how operational equipment must be constructed to prevent ignition in potentially explosive atmospheres.

Intrinsically Safe Pressure Measurement Technology from KELLER

In addition to devices with explosion protection type d (flameproof enclosure) and type ec (increased explosion safety), KELLER AG für Druckmesstechnik mainly manufactures pressure transmitters, level meters, and digital pressure gauges with explosion protection type i (intrinsic safety). Devices certified as intrinsically safe limit energy in such a way that neither sparks nor thermal effects can cause an explosion in explosive atmospheres.

KELLER is an international company that is not limited to the European market only. For this reason, the manufacturer of pressure measuring instruments offers a wide range of certificates that may be suitable for specific products worldwide:

International: IECEx   

International Electrotechnical Commission

System for use in explosive atmospheres

Europe: ATEX:

Explosive atmospheres

United Kingdom: UKCA

UK Conformity Assessment

Russia: EAC

Eurasian Conformity

There are also special licenses for:

North America: FM Approved

Property Loss Prevention Certificate

North America: UL

Underwriters Laboratories

Canada: CSA

Canadian Standards Association

Korea: KCs

Korea Certification Safety

All explosion-proof devices manufactured by KELLER are easily recognizable by a special marking. This marking contains designations that include, among other things, information for explosive atmosphere mixtures of explosion-proof devices:

• Ex mark for ATEX
• Type of explosion protection (e.g., ia)
• Mixture category IIA, IIB, or IIC
• Temperature class (e.g., T4-T6)
• Device protection level (e.g., Ga)
• Licensing department
• License number
• X for special conditions of safe use, described in more detail in the application manuals

Explosion-proof devices in action

Devices suitable for potentially explosive atmospheres have a very wide range of applications. KELLER AG has been producing explosion-proof pressure measuring devices since 1988. As a result of this invaluable experience, KELLER's certified products have gained recognition in many fields. The following four examples clearly demonstrate familiar everyday situations that share one main task. In all application areas, volume, fill level, or flow of a container is measured and controlled using pressure. This common task is associated with a wide range of hazards in potentially explosive atmospheres:

Automotive industry: Painting robots

During spraying, combustible mixtures can form from the suspension in the nozzle.

Aviation industry: Technology for transporting and supplying fluids for de-icing machines

De-icing is carried out with a fluid that consists of at least 50% flammable glycol and water.

Oil industry: Monitoring fill levels at gas stations

At gas stations, there is a risk that an electric spark could cause an explosion of the gas atmosphere.

Chemical industry: Monitoring the distribution of chemicals

Warehouses belonging to chemical companies and distributors store many different containers with chemicals containing various explosive and harmful substances.

Measurement and transmission

If devices are used in hard-to-reach places, measurement results cannot always be processed on site. For such cases, KELLER offers remote transmission devices that send measurement results to a server or the cloud. Recorded data and measurement results can be retrieved and analyzed using the customer's application or KELLER's own KOLIBRI Cloud portal.

Remote data transmission devices, such as ARC1-Box-SB by KELLER, are not explosion-proof by themselves. Therefore, modules used in potentially explosive environments must be installed outside the hazardous area. Remote data transmission devices for certified explosion-proof instruments have intrinsic safety barriers that limit the electrical power supplied to the connected intrinsically safe device. This barrier prevents explosions and ensures the required explosion protection.

The future of explosion protection

Currently, KELLER is developing a new type of radio transmission device that transmits data via LoRaWAN or NB-IoT (Internet of Things) networks and can be installed in potentially explosive environments. This development will make explosion protection even safer while simplifying the installation of pressure measurement equipment in hazardous zones.

Remote data transmission via LoRaWAN or NB-IoT networks