Intrinsically safe radios: a multi-vendor comparison for Zone 1 & Zone 2 hazardous areas

Intrinsic safety (Ex i) is a protection concept defined in IEC 60079-11. It works by limiting the electrical energy available in a circuit so that any spark or thermal effect is too weak to ignite a surrounding explosive atmosphere. Unlike flameproof (Ex d) enclosures that contain an explosion, intrinsically safe equipment prevents ignition from occurring in the first place.

For a two-way radio to be certified as intrinsically safe, every energy-storing component — the battery, the antenna, the speaker-microphone — must be assessed as part of the certification. The Notified Body (for ATEX) or ExTL (for IECEx) evaluates the complete system, not just the radio body. This is why mixing certified and uncertified accessories invalidates the protection.

The two relevant levels of intrinsic safety for portable radios are Ex ia (safe with two faults — required for Zone 0) and Ex ib (safe with one fault — sufficient for Zone 1 and Zone 2). Nearly all commercial two-way radios carry Ex ib IIC T4 or T3 certification.

Hazardous area classification determines which radio certification you need. Zone 1 areas contain explosive atmospheres during normal operation on an occasional basis. Zone 2 areas see explosive atmospheres only briefly and abnormally.

Zone 1 requires Ex ib or Ex ia protection. Most ATEX-certified radios on the market carry Ex ib IIC T4 Gb marking, which covers Zone 1 and Zone 2 for all gas groups. A Zone 1 radio can always be used in Zone 2, but not the reverse.

Zone 2 permits Ex nA (non-sparking) or Ex ec protection in addition to Ex i. These are less restrictive protection concepts and result in lower-cost equipment, but they cannot enter Zone 1 areas. If your site has mixed zones, standardising on Zone 1 rated equipment simplifies logistics and eliminates the risk of a Zone 2 radio being carried into a Zone 1 area.

Every ATEX or IECEx certified radio carries a marking string that encodes its protection level. A typical marking looks like: Ex ib IIC T4 Gb. For a detailed breakdown of what each element means, see the Ex markings reference on exknowledge.com.

The battery is the largest energy source in an intrinsically safe radio and is always part of the Ex certification. Using a non-certified battery — even one that is physically compatible — voids the radio's Ex certificate and creates an ignition risk.

Certified batteries carry their own Ex marking and are listed on the radio's certificate as "associated apparatus." When procuring replacement batteries, confirm the battery model number appears on the current version of the radio's ATEX or IECEx certificate. Certificates are revised when new batteries are added.

The same principle applies to all accessories used in the hazardous area: speaker-microphones, earpieces, and carrying solutions. Chargers and programming cables are typically used outside the hazardous area and do not require Ex certification, but confirm this with the manufacturer's documentation.

Battery charging inside the hazardous area requires a certified charging station. Most vendors offer multi-unit chargers rated for Zone 2 (Ex ec or Ex nA) but not Zone 1 — batteries are removed from the radio and transported to a safe area or Zone 2 charging station.

The right intrinsically safe radio depends on the operating environment and communication requirements. Below are common deployment scenarios and the features that matter most in each.

Upstream oil and gas. Offshore platforms and onshore wellpads require IIC T4 Gb certification (hydrogen present), IP68 ingress protection, and GPS for lone worker tracking. DMR Tier III trunking is preferred on large platforms where channel congestion is a concern. Battery life of 12+ hours covers a full offshore shift without mid-shift swaps.

Downstream refining and petrochemical. Refineries typically have mixed Zone 1 and Zone 2 areas across large sites. Standardising on Zone 1 radios eliminates the risk of carrying a Zone 2 unit into the wrong area. AES-256 encryption is increasingly required for security compliance. Multi-site operations benefit from DMR repeater networks that allow wide-area coverage without cellular infrastructure.

Chemical manufacturing. Chemical plants often have diverse gas atmospheres — ethylene (IIB), hydrogen (IIC), and ammonia (IIA) may all be present in different process areas. Certifying all radios to IIC eliminates the need to track which radio can enter which area. Noise levels in pump houses and compressor rooms can exceed 95 dB, making speaker-microphone accessories or Bluetooth headset integration essential.

Mining and tunnelling. Underground mines require Group I (firedamp) certification, not Group II. Check that the radio carries both Group I and Group II markings if it will be used in both surface and underground facilities. Rugged construction, high drop ratings, and loud audio output are critical in underground environments where ambient noise is high and visibility is limited.

Most intrinsically safe radios available today support DMR (Digital Mobile Radio), but analogue models remain in service. The choice between protocols affects procurement, interoperability, and long-term infrastructure costs.

DMR doubles the capacity of each 12.5 kHz channel by using two time slots (TDMA), provides AES-256 encryption, enables GPS location services, and supports text messaging and telemetry. DMR radios are backwards-compatible with analogue systems in most cases, allowing phased migration. The three DMR tiers — Conventional (Tier II), Trunked (Tier III), and Direct Mode — offer flexibility from simple two-radio setups to enterprise-wide trunked networks.

Analogue radios are simpler and less expensive, but offer no encryption, no GPS, and single-channel-per-frequency operation. They remain a practical choice for small sites with few users and no security requirements. However, analogue repeater infrastructure is being phased out by most vendors, and replacement parts are becoming harder to source. New deployments should default to DMR unless there is a specific legacy interoperability requirement.

Before deploying any intrinsically safe radio, verify its certification is current and covers the conditions at your site. Here is a step-by-step process:

1. Identify the certificate number from the radio's nameplate or datasheet. ATEX certificates follow the format Baseefa04ATEX0123X; IECEx certificates follow IECEx BAS 04.0012X.
2. Check the IECEx database at iecex.com. Search by certificate number or manufacturer. The database shows the current issue number, any conditions of certification, and whether the certificate is active or withdrawn.
3. Match the Ex marking on the certificate to your site's zone classification, gas group, and temperature class. A radio certified Ex ib IIC T4 Gb covers Zone 1, all gas groups, and auto-ignition temperatures above 135 °C.
4. Confirm all accessories are listed on the certificate. The schedule of the certificate lists every battery, antenna, and accessory approved for use in the hazardous area.
5. Check for conditions. Certificates may include Special Conditions (marked with an "X" suffix) that impose usage restrictions — for example, limits on charging current or requirements for specific cable types.

For ATEX certificates, the issuing Notified Body (e.g., Baseefa, CML, DEKRA) maintains the master record. The certification process reference on exknowledge.com explains the full ATEX and IECEx certification workflow.