Optical fibers in hazardous areas

P-Ex OTR opis Module

 

A myth that persists.

A common myth in many companies states that "Once laid, a fiber optic cable only needs to fulfill its purpose: transporting data from A to B"—which usually works without any problems. Unfortunately, this persistent myth also implies that the light in the fiber is safe even in hazardous areas and that no further concerns need to be raised.

Because optical fibers (fiber optic cables) are currently considered safe and harmless, they are used in many companies today for hazard prevention when it comes to data cabling in hazardous areas. The dangers posed by power cables are generally known, and these are installed with appropriate protection, or other measures are taken, such as intrinsic safety. However, when operators of facilities are asked about the use of fiber optic cables in hazardous areas, they often react with incomprehension or shrugging, and when the relevant standard is mentioned, they point to years of operation without any significant damage.

In hazardous areas, an unprotected fiber optic cable that is accidentally damaged during a subsequent installation, an improperly executed splice of the fiber optic cable, or a carelessly disconnected data connector can lead to immense damage. It can even cause an explosion. While light does not actually have enough energy to ignite a gas/air mixture (with the exception of blue lasers with extremely high energy density), it can heat deposits or other suspended particles to such an extent that a reaction occurs. Therefore, the standard IEC/EN 60079-28:2015 exists, which deals precisely with this issue.

In summary, three different approaches can be considered as possible solutions:

• Optical systems with locking mechanism (op sh)

• Protected optical radiation (op pr)

• Inherently safe optical radiation (op is)

The first variant is primarily intended for use in laboratories and small plant sections, as it allows the entire system or a defined area to be shut down very quickly upon the presence of a corresponding gas mixture. However, this protective measure, called op sh (Optical Radiation with Interlock), is not suitable for production plants, as the shutdown could cause significant damage.

The next practical solution would be the protected installation of the fiber optic cables. This option is called op pr (protected optical radiation). However, due to local conditions, it can quickly become an expensive project, as the fiber must be protected along its entire length. This may involve skipping different floors, passing through various fire compartments, and, importantly, the complete equipotential bonding of the conduit to be protected. All in all, this requires extremely careful planning and correspondingly monitored execution.

The simplest and most cost-effective solution is to limit the light energy output to below 35 mW. This prevents ignition or explosion due to the energy required to ignite various gases. This solution is called op is (inherently safe optical radiation, similar to Ex "i" for copper cabling). Modules are simply inserted into the transmitting and receiving lines to ensure that the 35 mW limit is never exceeded in the event of damage. It is crucial that the line is protected at both ends when transmitting data, not just receiving it. The power supply should also be carefully considered. This means that a defective or faulty power source must not impair the laser diode's function.

Therefore, the P-Ex-OTR opis series media converters from PRIMATION Systemtechnik have a corresponding protection circuit. Klick to find out more...

Due to their small dimensions and compact design, installation in existing systems or new installations is usually straightforward. If you have any questions regarding device selection, please contact us. We are happy to offer support and advice, even during the planning phase.