Figure 1. Petrochemical and refining facilities are a typical use-case for intrinsically safe sensors. (Image: Monnit)

An apparatus such as a wireless sensor used in a hazardous location must be designed and certified to meet the required safety standards. Those standards are amplified when the environment and work already deemed inherently hazardous duty is done in areas where explosive (Ex) atmospheres are anywhere from always to only rarely present.

Risks from Explosive Atmospheres are in Many Industries

It’s easy to consider explosive atmospheres in the oil and gas industry as hazardous locations for electrical equipment — at petrochemical and refining facilities, field and offshore drilling operations, and gas stations. But explosive atmospheres with flammable and combustible gases, vapors, dust, powders, and fibers can be present in other industrial applications — such as chemical production, pharmaceutical and cosmetics manufacturing, food processing, power generation, mining, construction, and architectural woodworking.

By law and good sense, everything and everyone must be safeguarded and certified according to the safety standards for these hazardous locations. What’s the risk? One tiny spark or overheated device could ignite an explosion, causing damage, injury, or even loss of life.

Engineers Make Critical Design Decisions

For operations in explosive or potentially explosive atmospheres, engineers must ensure each process, system, and apparatus meets or exceeds safety regulations from design to production to installation and operation. Engineers can use several protection methods against explosive atmospheres to create safe hazardous duty sensors.

  • Some methods involve electronics segregation like encapsulating electronics in epoxy, covering electronics in non-flammable oil or powder, or sealing electronics in a vacuum chamber.

  • Another method is to use an explosion-proof enclosure to confine any explosion inside its robust, rugged housing.

  • The intrinsic safety method limits an apparatus’s electrical and thermal energy by the laws of physics from creating a spark or hot spot sufficient to ignite an explosion during normal operation and fault conditions anywhere within the circuitry.

These methods aren’t mutually exclusive, but in our view, intrinsic safety is the gold standard.

Whatever the protection method, an engineer’s job is to plan and design products using safety standards like those of the International Electrotechnical Commission (IEC). The IEC System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres (IECEx) ensures engineers, manufacturers, and equipment meet strict safety requirements. We chose IECEx as the standard system and epoxy encapsulation to design our intrinsically safe ALTA-ISX® Sensors.

IECEx Certification for Intrinsically Safe Sensors

Figure 2. Refinery operations being monitored with IECEx-certified ALTA-ISX Sensors. (Image: Monnit)

To be IECEx-certified, sensors must meet multiple design standards and a production standard. The design standards include the general IEC 60079-0 standard and at least one protection method-dependent standard such as IEC 60079-11 for intrinsic safety. The production standard is the International Organization for Standardization (ISO)/IEC 80079-34, similar to ISO 9001 with quality management system additions for hazardous locations.

Engineers can purchase the IECEx standards to guide design and conformity. Then, they can hire a third-party IECEx Certification Body (ExCB) to test and verify the design against the standards. The ExCB requires you to submit design information, such as schematics, Gerber files, and a bill of materials (BOM); and production information, such as quality management system documents for manufacturers.

The designer should know that an IECEx production certificate locks the design documents down to the make and model of each surface mount resistor identified in the BOM. The ExCB will also need to review and approve a safety manual outlining the sensor’s safe installation, use, and maintenance requirements.

Being IECEx-certified allows you to sell sensors internationally without re-testing and re-certifying for every participating country. This helps manufacturers reduce testing and certification costs.

The Path to be IECEx-Certified

Figure 3. Propane tanks being monitored with IECEx-certified ALTA-ISX Sensors. (Image: Monnit)

We recommend following these steps to achieve IECEx certification for intrinsically safe, hazardous duty sensors.

Step 1: Determine the Nature of the Sensor’s Hazardous Locations

To outline your sensor’s design, the biggest question you need to answer is: Where will the sensor be placed? This is an essential first step because it determines which provisions of the standards will apply to your design. Related questions for your sensor design include:

  • To what potentially explosive gases and vapors will the sensor be exposed?

  • What percentage of the time are the sensors likely exposed to those gases and vapors?

  • How hot will the ambient temperature be in the environment?

  • Will there be dust, powder, or fibers present?

  • Will the sensor be used in a mine?

Plan for the worst-case scenario of what your sensor may be exposed to in a hazardous location. When you succeed, the IECEx certification code on your sensor’s label will explain the compliance level for each question.

For example, our ALTA-ISX Sensors are IECEx-certified with code: Ex ib IIA T3 Gb. Essentially:

  • The “Ex” means the sensor is IECEx-certified.

  • The “i” means the design is intrinsically safe.

  • The “b” indicates it is safe against a single fault of an open or short anywhere in the circuitry, qualifying the sensor for use in IEC Zone 1 and Zone 2 areas.

  • The “IIA” defines the group of gases (propane, gasoline, methane, and others) for which the sensor is designed.

  • The “T3” indicates that auto-ignition isn’t possible for gases within group IIA that also have an auto-ignition temperature above 300°C, as long as the ambient temperature doesn’t exceed 40°C.

  • The “Gb” means the sensor is safe for explosive gases and vapors but not for dust or deployment in a mine.

Step 2: Design With Critical Considerations in Mind

Designing a sensor that monitors 24/7 in hazardous locations requires paying relentless attention to critical considerations. Possibly the most challenging concern is applying constant fault analysis throughout the circuitry. You have to keep the circuitry’s voltages and currents below problematic levels, considering what could happen if there was a short or open anywhere. Plus, the sensor’s hazardous location can complicate the design to accommodate two faults anywhere in the circuitry.

Voltage and Current

The circuitry’s high voltage can cause a spark. Redundant Zener diodes can keep voltages at acceptable levels by capping voltage when levels are exceeded. Voltage capping design measures can be key when you add a boost converter.

Similarly, the circuitry’s high current can create a hot spot. Redundant resistors can keep current at acceptable levels, but that may involve tradeoffs because the added power dissipation might cause excessive heating. As with all components, resistor selection and use are critical for balancing current and voltage requirements without undue heating or sparking.

The Battery and Stored Energy

Careful consideration should be paid to the battery. What happens if the battery is shorted? Is there enough internal resistance to prevent an issue? The ExCB will test the battery and confirm its performance limitations and what happens if it releases a sudden surge of energy. You must also ensure your safety manual strictly communicates the battery requirements. Although it’s a lesser concern, you should install redundant diodes near the battery to account for the human error of installing it backward.

Consider stored circuitry energy, which one or more fault conditions could release. The ways capacitors and inductors release energy can get complicated. But complexity doesn’t have to breed complexity. A simple approach is to add up all capacitances and inductances. This can help ensure they remain below acceptable levels based on the answers to your original questions about the sensor’s possible hazardous locations.

The energy released by the sensor’s radio module, which depends on capacitors and inductors to produce carrier waves must be considered, as should the inductance and capacitance issues that might arise with sensor leads and a transducer. The transducer must be certified to be part of the sensor.

Trace Widths and the PCB

Consideration must also be given to the trace widths to dissipate heat on the printed circuit board (PCB) and clearance and creepage to prevent arcs. You should set rules for these concerns in your layout software. All of these considerations can make real estate on the PCB a significant concern as you design to make room for the added resistors, diodes, traces, etc., to ensure the sensor is intrinsically safe.

Step 3: Mitigate Design Challenges with an Internal Quality Team

It’s surprising how complex the process can get once you combine all the critical considerations. It can be like playing an extreme game of Tetris. This version is best played with multiple participants who can catch each other’s oversights. The IECEx certification process is easier when working with a team of engineering, testing, and production professionals.

In hindsight, after getting three of our ALTA-ISX Sensors certified, we benefitted by designing our sensors for Zone 1 hazardous locations first, not Zone 0. Why? The IECEx certification level we pursued and achieved met our customer’s needs. Now, that experience is helping us level up to handle higher-risk requirements for Zone 0 hazardous locations using double-fault analysis for additional intrinsically safe IECEx-certified sensors.

This article was written by Stephen Preston, Electrical Engineer at Monnit (South Salt Lake, UT). For more information, contact Mr. Preston at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit here .