Electrical Safety in Potentially Explosive Atmospheres

Additional and Safety Power Supplies

A normal supply is provided by a primary supplier. An additional supply is provided by the same company, where independent energy distribution facilities are available. Additional supplies are classified as follows:

• Relief Supply: Limited to receiving 15% of the total power contracted for the normal supply.
• Backup Supply: Limited to receiving at least 25% of the power contracted for the normal supply.
• Duplicate Supply: Capable of maintaining service at more than 50% of the total power contracted for the normal supply.

Emergency Lighting Systems

The purpose of emergency lighting is to ensure illumination during a failure of the normal lighting system. It illuminates premises and access to exits for a potential public evacuation or provides light in other designated areas.

Types of Emergency Lighting

• Escape Lighting: The part of emergency lighting that ensures the recognition and use of evacuation routes while the premises are or may be occupied.
• Ambient or Anti-Panic Lighting: The part of emergency lighting designed to prevent panic by providing adequate ambient light, allowing occupants to identify and access evacuation routes and see obstacles.
• High-Risk Area Lighting: The part of emergency lighting that ensures the safety of individuals engaged in potentially hazardous activities. It allows work to be interrupted safely for the operator and other occupants.

Hazardous Area Protection Methods

• Flameproof Enclosure "d": Components that could ignite an explosive atmosphere are placed within an enclosure strong enough to withstand the pressure of an internal explosion and prevent its transmission to the surrounding atmosphere.
• Oil Immersion "o": Electrical equipment or its parts are immersed in a protective liquid, preventing any explosive atmosphere on the liquid's surface or around the enclosure from being ignited.
• Intrinsic Safety "i": Prevents any spark or thermal effect produced under normal operating conditions from causing an ignition.
• Intrinsic Safety Systems: A set of interconnected electrical equipment where the circuitry is designed for use in potentially explosive atmospheres.

Equipment Categories for Hazardous Areas

• Category 1: Ensures a very high level of protection.
• Category 2: Ensures a high level of protection.
• Category 3: Ensures a normal level of protection.

Basic Security Measures

Achieving basic security involves several key principles:

• Using equipment constructed and selected according to specific rules.
• Adopting special security measures for installation, inspection, maintenance, and repair.
• The operation, conservation, and maintenance of the facility and its components must be kept within strict limits.

Site Classification for Explosive Atmospheres

To establish the requirements for electrical installation components, sites with potentially explosive atmospheres are divided into two classes:

• Class 1: The risk is due to flammable gases, vapors, or mists.
• Class 2: The risk is due to combustible dust.

Class 1 Site Zones

This class includes sites where gases, vapors, or fumes may exist in sufficient quantities to produce explosive or flammable atmospheres. Three zones are distinguished:

• Zone 0: A location where an explosive atmosphere is present continuously, for extended periods, or frequently.
• Zone 1: A location where an explosive atmosphere is likely to occur occasionally in normal operation.
• Zone 2: A location where an explosive atmosphere is not likely to occur in normal operation.

Class 2 Site Zones

This class includes sites where combustible dust is or may be present. Three zones are distinguished:

• Zone 20: A location where an explosive atmosphere, in the form of a cloud of combustible dust in the air, is present continuously, for extended periods, or frequently.
• Zone 21: A location where an explosive atmosphere from a cloud of combustible dust is likely to occur occasionally in normal operation.
• Zone 22: A location where an explosive atmosphere from a cloud of combustible dust is not likely to occur in normal operation, and if it does, it will only persist for a short time.

Installation Prescriptions and Conditions

Proper documentation and adherence to conditions are critical for safety and compliance. This includes:

• Documentation: Site classification and representative plans.
• Equipment Appropriateness: Ensuring the equipment category is suitable for the specific locations and zones.
• Instructions: Following guidelines for implementation, connection, and installation of equipment.
• Special Conditions: Adhering to any special conditions for equipment installation and utilization.