What is Intrinsic Safety? Definition, Working Principle, Standards and Applications

Intrinsic safety is one of the most widely used explosion-protection techniques for electrical and instrumentation systems installed in hazardous areas. It is specifically designed to prevent ignition by controlling the electrical and thermal energy available in a circuit.

This guide explains what intrinsic safety is, how it works, applicable standards, equipment examples, benefits, and where it is used, in a clear and practical manner.

Intrinsic Safety Definition

Intrinsic safety (IS) is a protection technique that ensures electrical equipment and wiring used in hazardous areas cannot release sufficient electrical or thermal energy to ignite flammable gases, vapors, or combustible dust.

According to IEC 60079-11, intrinsic safety is defined as:

A type of protection based on the restriction of electrical energy within equipment and interconnecting wiring exposed to a potentially explosive atmosphere to a level below that which can cause ignition by sparks or heating effects.

In simple terms, intrinsic safety prevents explosions by limiting energy, rather than containing an explosion after it occurs.

What is the Purpose of Intrinsic Safety?

The main objective of intrinsic safety is to eliminate ignition sources in hazardous locations by ensuring that:

• Sparks cannot release enough energy to ignite gases or dust
• Electrical components cannot reach ignition temperatures
• Fault conditions do not create unsafe energy levels

This makes intrinsic safety especially suitable for measurement, control, and monitoring circuits.

1. A spark
2. A hot surface.

• The intrinsic safety approach simplifies the circuits and minimizes the cost of installation over other protection methods.
• During the installation of plant equipment in a location where a fire is a risk, an engineer has two options. He must

1. Employ explosion-proof techniques.
2. Utilize an intrinsically safe design approach.

• Generally, equipment certified with intrinsic safety is slightly more expensive than non-intrinsic equipment.
• In the design of an intrinsic safety barrier, a Zener diode is used to limit voltage, resistors are used to restrict current and a fuse, none of which are expensive.
• Being intrinsically safe in terms of electrical means limiting the flow of current or preventing sparks in a hazardous environment.

Intrinsic Safety Barriers and Components

Intrinsic safety systems rely on protective components to limit energy.

Common Intrinsic Safety Barrier Components

• Zener diodes to clamp voltage
• Resistors to limit current
• Fuses to protect against excessive faults
• Galvanic isolators for electrical separation

These barriers are installed in the safe area, while field devices operate in the hazardous area.

Equipment considered for use in hazardous areas with intrinsically safe barriers includes:

1. 4-20 mA DC Two Wire Transmitters.
2. Thermocouples.
3. RTDs.
4. Strain Gages.
5. Pressure, Flow, & Level Switches.
6. I/P Converters.
7. Solenoid Valves.
8. Proximity Switches.
9. Infrared Temperature Sensors.
10. Potentiometers.
11. LED Indicating Lights.
12. Magnetic Pickup Flow meters.

Describe the types of intrinsically safe levels:

NEC 70 intrinsically safe levels are classified as:

Class I: The Class I environment consists of flammable gasses and vapor such as gasoline, hydrogen, natural gas propane, ethanol, or methane.

Class II: The Class II environment consists of combustible dust such as the dust of metal and its alloys, charcoal, carbon black, flour, plastics, grains, and wood. These dust exist under normal and abnormal operating conditions.

Class III: Class III consists of flying objects or fibers.

NEC: National Electrical Code

How does an intrinsic safety system work?

• An intrinsic safety system behaves as an energy barrier by restricting the voltage and current signals in a hazardous environment.
• These systems also check the total amount of energy in the hazardous environment.
• Ensuring lower energy to ignite flammable gasses or particles.
• Avoiding ignition assumes reducing both the available power and the maximum temperatures.
• The supplied voltage and current must be less than 29V and 300 mA.
• In a simpler view is to say that power must be less than 1.3 W.
• The equipment installed must be certified as intrinsically safe before using in a hazardous area.
• These safety barriers protect the system. But these must be mounted outside of the hazardous area designated as safe where the hazard is not present.

Intrinsic Safety Energy Limits

To qualify as intrinsically safe, a circuit must typically comply with the following limits:

• Voltage: less than 24 VDC
• Current: less than 100 mA
• Power: less than 1.3 W

These values ensure that even under fault conditions, the energy is insufficient to ignite a hazardous atmosphere.

Intrinsic Safety vs Explosion-Proof Protection

Intrinsic safety and explosion-proof protection are fundamentally different approaches.

Intrinsic Safety

• Prevents ignition by limiting energy
• Allows live maintenance
• Uses lightweight enclosures
• Lower installation and maintenance cost

Explosion-Proof Protection

• Contains explosions inside heavy enclosures
• Requires rigid conduit systems
• Higher installation cost
• Limited maintenance flexibility

Intrinsic safety is often preferred for instrumentation and control circuits.

Note that most of the instrumentation devices used to consume only 24V and can often be designed to draw a current of less than 500 mA which is reasonably sufficient to meet IS certification in many situations.

Benefits of Intrinsic Safety Systems

Intrinsic safety system or intrinsic safety barriers provides several advantages when electrical or instrumentation equipment must be placed in a hazardous environment.

1. Provides a safe working environment and protects from the risk of explosion
2. The cost of explosion-proof enclosures is reduced.
3. Saves cost by using standard instrumentation cables.
4. Insurance premiums can be reduced when risks are minimized

Limitations of Intrinsic Safety

Despite its advantages, intrinsic safety has limitations:

• Not suitable for high-power equipment
• Cannot be used for motors, heaters, or lighting circuits
• Requires careful system design and certification

For high-power applications, alternative protection methods are required.

What voltage is considered intrinsically safe?

Intrinsic safety is considered the technique of protection for control and instrumentation circuits.

For intrinsically safe

1. The nominal voltage is considered to be 24 VDC or less.
2. The current must be less than 100 mA.
3. Power must be less than 1.3 W.

Where is intrinsic safety used?

Intrinsic safety accessories are used in hazardous areas that have a dangerous and heavy concentration of combustible gases that may be highly flammable in petrochemical refineries and mining industries.

Intrinsic safety is a highly effective explosion-prevention technique that protects hazardous areas by limiting electrical and thermal energy. It is widely used for instrumentation and control systems because it enhances safety, reduces costs, and simplifies maintenance while complying with international safety standards.