Hazardous areas require carefully selected and certified equipment to ensure electrical devices do not become potential ignition sources. Where flammable gases, vapours or dusts may be present, specialist explosion protection methods are used to minimise risk, protect personnel, and maintain safe and reliable operations.
Two of the most common protection concepts used within hazardous areas are Ex d (Flameproof) and Intrinsically Safe (IS). Although both methods are designed to prevent ignition risks, they achieve this in very different ways.
In this guide, we’ll cover:
• What Ex d is
• What Intrinsically Safe (IS) means
• The key differences between Ex d and IS
• When to use Ex d or IS
• Can Ex d and IS be used together?
• Common misconceptions
Contents
- 1 What is Ex d?
- 2 What is Intrinsically Safe (IS)?
- 3 Hazardous Area Zones
- 4 Zone 0
- 5 Zone 1
- 6 Zone 2
- 7 Disadvantages of Intrinsic Safety
- 8 Ex d vs IS: Key Differences
- 9 When Should You Use Ex d?
- 10 When is IS a Better Choice?
- 11 Can Ex d and IS Be Used Together?
- 12 Common Misconceptions
- 13 Choosing the Right Protection Method
What is Ex d?
Ex d is a protection method used for electrical equipment installed in hazardous areas. Under IEC and ATEX standards, Ex d is commonly referred to as Flameproof protection. In North America, a similar concept is often referred to as Explosion Proof.
Rather than preventing an explosion from occurring, Ex d equipment is designed to contain an internal explosion and prevent it from igniting the surrounding hazardous atmosphere.
Ex d equipment uses a robust enclosure, commonly manufactured from materials such as aluminium or stainless steel. If a flammable gas enters the enclosure and ignites, the enclosure is designed to withstand the resulting pressure. Any escaping gases pass through carefully engineered flamepaths, which cool the gases before they reach the external atmosphere.
Characteristics of Ex d
• Suitable for higher-power electrical equipment.
• Commonly used for motors, switchgear, control panels, junction boxes, actuators and other equipment that may generate sparks or arcs.
• Designed to contain an internal explosion without transferring ignition to the surrounding environment.
• Extremely robust and suitable for demanding industrial applications.
Disadvantages of Ex d
• Equipment can be heavier and more expensive compared with non-hazardous area equipment.
• Enclosures can be larger and more difficult to install in some applications.
• Maintenance activities may require additional precautions, including ensuring equipment is isolated before opening within hazardous areas.
• Installation requires careful consideration of certification requirements.
What is Intrinsically Safe (IS)?
Intrinsically Safe (IS) is a protection technique designed to prevent ignition from occurring in the first place.
Instead of containing an explosion, IS systems limit the electrical and thermal energy available within a circuit to a level below that required to ignite a hazardous atmosphere, even under fault conditions.
Intrinsic Safety typically relies on:
• Energy limitation
• Zener barriers
• Galvanic isolators
• Current and voltage limiting devices
How Intrinsic Safety Works
The principle behind Intrinsic Safety is simple: keep electrical energy below the ignition threshold of the surrounding hazardous atmosphere.
- Low voltage and current levels reduce the possibility of ignition.
- Energy-limiting components prevent excessive power from reaching hazardous area devices.
- Zener barriers or galvanic isolators control the energy entering the hazardous area.
Because the available energy is limited below ignition thresholds, IS systems are particularly suited to instrumentation and monitoring devices installed in hazardous locations.
Hazardous Area Zones
Hazardous areas are classified according to the likelihood and duration of an explosive atmosphere being present.
Zone 0
An explosive gas atmosphere is present continuously, for long periods, or frequently.
Zone 1
An explosive gas atmosphere is likely to occur during normal operation.
Zone 2
An explosive gas atmosphere is not likely to occur during normal operation, and if it does occur, it will only exist for a short period.
Equipment selection also considers other factors, including gas groups, temperature classification, ambient conditions, and certification requirements.
Disadvantages of Intrinsic Safety
• Not suitable for high-power equipment such as large motors.
• System design requires detailed calculations and certification review.
• Modifications must be assessed to ensure certification remains valid.
• Cable lengths, device selection and system parameters may introduce design limitations.
Ex d vs IS: Key Differences
| Ex d | Intrinsically Safe (IS) |
|---|
| Key Function | Contains an internal explosion within a certified enclosure | Prevents ignition by limiting electrical and thermal energy |
| Equipment Type | Higher-power equipment and electrical components | Low-power instrumentation and field devices |
| Protection Method | Robust flameproof enclosure | Energy limitation and certified safety barriers |
| Size | Generally larger and heavier | Typically smaller and lighter |
| Typical Applications | Motors, panels, junction boxes, actuators | Gas detectors, transmitters, sensors and instrument loops |
When Should You Use Ex d?
Ex d protection is commonly selected for equipment that may generate sparks, arcs or high temperatures during operation.
Typical applications include:
• Electric motors
• Motor starters
• Junction boxes
• Actuators
• Switchgear
• Control panels
Ex d is widely used in Zone 1 and Zone 2 hazardous areas where robust equipment protection is required.
When is IS a Better Choice?
Intrinsic Safety is often preferred where low-power instrumentation is installed within hazardous areas.
Typical applications include:
• Gas detectors
• Pressure transmitters
• Temperature sensors
• Flow meters
• Instrument loops
IS systems can also provide maintenance advantages, as technicians may be able to carry out certain inspection and calibration activities without removing equipment from service, depending on the system design and certification requirements.
Can Ex d and IS Be Used Together?
Yes. Combining Ex d and Intrinsically Safe protection methods is common throughout the oil and gas, chemical processing and wider industrial sectors.
Examples include:
Ex d Enclosures with IS Components
A flameproof enclosure may contain higher-power components such as power supplies or control hardware. Intrinsic Safety barriers inside the enclosure can then provide safe signals to field instruments located in hazardous areas.
IS Components Within Ex d Equipment
An Ex d motor or actuator may include intrinsically safe position switches or feedback sensors while the main power components remain protected by flameproof construction.
Ex d Field Enclosures for IS Barriers
Where barriers or galvanic isolators cannot be installed in a safe area, they may be installed within a suitably certified Ex d enclosure located within a hazardous area.
Common Misconceptions
Is IS Safer Than Ex d?
Both protection methods are considered safe when correctly selected, installed and maintained. The difference is that Ex d contains an explosion if one occurs, while Intrinsic Safety prevents ignition by limiting available energy.
Why Do IS Systems Need Barriers?
Safety barriers limit voltage and current entering hazardous areas, ensuring field devices remain incapable of creating an ignition source.
Do All Gas Detectors Use Ex d?
No.
Fixed gas detectors may use Intrinsically Safe, Ex d Flameproof, or other certified protection methods depending on the detector design, hazardous area classification, installation philosophy and application requirements.
Which is Cheaper: IS or Ex d?
The overall cost depends on the application, installation method, certification requirements and system design. IS systems can often provide cost benefits for instrumentation applications due to lighter equipment and simplified installation requirements, while Ex d may be more suitable for higher-power equipment.
Choosing the Right Protection Method
Both Ex d and Intrinsically Safe (IS) are proven explosion protection methods used throughout hazardous industries, but they achieve safety in fundamentally different ways.
Ex d equipment is designed to safely contain an internal explosion within a robust enclosure, while Intrinsically Safe equipment prevents ignition by limiting electrical energy below hazardous levels.
Choosing the correct protection method depends on:
• Hazardous area classification
• Equipment power requirements
• Detector and instrument selection
• Maintenance requirements
• Installation considerations
• Overall system design
In many oil and gas, chemical processing and industrial facilities, both protection methods are used together to create safe, compliant and reliable installations.
For fixed fire and gas detection systems, selecting the correct protection concept is just as important as selecting the right detector. Understanding the differences between Ex d and Intrinsically Safe equipment helps ensure the correct technology is applied for each environment.
At Protex Systems, we support the selection and application of fire and gas detection solutions for hazardous environments. From detector selection and hazardous area considerations through to system design and optimisation, our focus is ensuring the right technology is applied for the specific risks and operating conditions of each facility.
