Understanding Flameproof Enclosures
(Ex ‘d’) in Hazardous Areas

Author: Luke Worth

Hazardous areas—also referred to as explosive atmospheres—are common in many industries, arising from flammable liquids, vapours, gases (e.g., petrol, ethanol, hydrogen), and combustible dusts (e.g., flour, sugar, wood filings). While these materials are vital to countless industrial processes, they also pose significant safety risks.

Electrical equipment in these environments is a particular hazard, as it can generate heat or sparks capable of igniting explosive atmospheres, potentially leading to catastrophic events. To mitigate these risks, such equipment must adhere to strict safety standards, ensuring its safe operation in hazardous areas.

Among the various protection methods available, Flameproof Enclosures, marked as Ex ‘d’, are a widely used technique. This article simplifies the concept of flameproof enclosures, outlining how they work and key considerations for their use.

Disclaimer:

This article provides general information to raise awareness about flameproof enclosures. Only qualified and trained professionals should install, repair, or maintain flameproof enclosures. For assistance, consult a licensed electrician or electrical engineer specializing in hazardous areas.

What Are Flameproof Enclosures[1] (Ex ‘d’)?

Flameproof enclosures are one of the oldest and most widely used techniques for hazardous area protection. They are designed to contain internal explosions within the enclosure and prevent flames, sparks, and hot gases from escaping and igniting the surrounding atmosphere.

Unlike some other protection methods, flameproof enclosures are not gas tight. Instead, they:

Withstand the pressure generated by internal explosions.

Direct and cool hot gases through a flame path so that by the time they exit the enclosure, they are no longer capable of igniting the external atmosphere.

These enclosures are easy to identify due to their robust construction, thick metal walls, and, often, multiple fasteners.

The Role of the Flame Path

A critical component of a flameproof enclosure is the flame path—a precisely engineered gap within the enclosure. If an explosion occurs inside, the flame path ensures that flames and hot gases are cooled and starved of oxygen before they exit.

To achieve this, the lengths of the paths and the gaps between machined surfaces are rigorously specified. Damaging or obstructing the flame path during installation or maintenance can compromise the protection, leading to a serious safety hazard. For example, using a screwdriver to pry open an enclosure lid could scratch the flame path and render the enclosure non-compliant.

Here’s a video demonstrating an Ex ‘d’ flameproof test and the potential consequences of flame path damage: Watch the Ex ‘d’ Flameproof Test

Key Considerations for Flameproof Enclosures

• Pressure Piling

Pressure piling occurs when an explosion in one part of a system compresses gases in another section, leading to a secondary, more intense explosion. For example, if two Ex ‘d’ enclosures are connected via a conduit without a properly rated barrier gland, the explosion can propagate, overwhelming the system's pressure limits.

• Maximum Power Dissipation

Flameproof enclosures often have limits on the heat that internal components can generate. To prevent improper use, many enclosures are component certified (indicated by a “U” suffix on the certificate). In such cases, only the manufacturer—or an approved professional—may position or install components inside the enclosure.

• Compliance with Standards

To ensure safety and compliance, all design and installation work must adhere to relevant standards, such as:

AS/NZS IEC 60079.0 – General Requirements

AS/NZS IEC 60079.1 – Flameproof Enclosures ‘d’

Conclusion

Flameproof enclosures (Ex ‘d’) are a trusted solution for hazardous area protection, offering flexibility to house various electrical components safely. While their robust design ensures safety, their size and weight can make them less practical in space-constrained environments.

At BOSCHETTI, we specialize in hazardous area services, including classification, design, and equipment installation. Our team of qualified engineers and electricians provides comprehensive solutions tailored to your needs, ensuring compliance with Australian standards and industry best practices.

Contact us today to learn how we can assist with your hazardous area requirements!

References

[1] AS/NZS 60079.14:2022 Clause 3.3.1 defines flameproof enclosure