Selecting a pressure transmitter for a hazardous location in North America requires more than an FM or CSA mark. Class, Division or Zone classification, gas group, temperature code, protection concept and the exact approval scope must all match the installation. This guide covers the key criteria — and leads directly into the sensor selector for a structured shortlist.
In North America, pressure transmitters for hazardous locations are typically approved under FM (Factory Mutual), CSA (Canadian Standards Association) or UL (Underwriters Laboratories). These approvals are based on NFPA 70 (NEC) and CSA C22.1 (CEC) standards and use a Class/Division classification system that differs from the European Zone system — though Zone-based marking (Class I Zone 0/1/2) is also recognised alongside Division marking in many jurisdictions.
Many transmitters carry both ATEX/IECEx and FM/CSA approval. For North American installations, For projects in the US or Canada, ATEX alone is generally not sufficient. Project specifications and local codes typically require equipment certified for North American hazardous locations, such as FM, CSA, UL or cULus. Always verify the exact approval required by the project and the authority having jurisdiction.
FM Approvals certifies equipment for hazardous locations. Widely specified in the US process industries. FM marking indicates the device has been tested to FM standards for the stated Class, Division and Group.
CSA Group certification is commonly used for Canadian and North American hazardous-location approvals. cCSAus or cULus markings may indicate certification for both Canada and the US.
UL certification is commonly used for hazardous-location equipment in the US. cULus marking indicates certification for both US and Canadian requirements. Often used alongside FM or CSA on the same device.
Safety Integrity Level per IEC 61508/61511. Separate from explosion protection. Available on selected FM/CSA-approved transmitters for safety instrumented systems.
The North American hazardous location system classifies the type of hazardous material (Class) and the likelihood of it being present (Division or Zone).
| Classification | Meaning | Typical protection concepts |
|---|---|---|
| Class I Division 1 | Flammable gas or vapour present under normal conditions | Intrinsically Safe (IS), Explosionproof (XP) |
| Class I Division 2 | Flammable gas or vapour present only in abnormal conditions | IS, XP, Nonincendive (NI) |
| Class II Division 1 | Combustible dust present under normal conditions | Dust-ignitionproof, IS |
| Class II Division 2 | Combustible dust present only abnormally | Dust-tight enclosures, IS |
| Class I Zone 0 | Continuous or long-duration explosive atmosphere | IS (ia), equivalent to IEC EPL Ga |
| Class I Zone 1 | Likely during normal operation | IS (ia/ib), Explosionproof, equivalent to EPL Gb |
| Class I Zone 2 | Not likely, only briefly | IS, Nonincendive, equivalent to EPL Gc |
Gas groups in the North American system use letters A through D (Class I) — where Group A covers acetylene, Group B hydrogen, Group C ethylene and Group D propane. The IEC gas groups IIA/IIB/IIC are not directly interchangeable with North American Groups A–D. As a rough orientation, IIC covers the most severe conditions, while Group B covers hydrogen and Group A acetylene. Always use the marking and certificate required for the specific installation — do not substitute one classification system for the other.
| Concept | Description | Typical use |
|---|---|---|
| Intrinsically Safe (IS) | Limits energy in the circuit so ignition cannot occur. Requires a certified IS barrier or isolator in the safe area. | 4–20 mA loops, Division 1 and Division 2, Zone 0/1/2 |
| Explosionproof (XP) | Enclosure contains any internal ignition. Heavier construction, suitable for higher power. | Class I Division 1, Zone 1 |
| Nonincendive (NI) | Not capable of igniting a specific hazardous atmosphere under normal operation. | Class I Division 2, Zone 2 only |
| Purged/Pressurised (PX/PY/PZ) | Enclosure is purged with clean air or inert gas to prevent hazardous atmosphere entry. | Panels and enclosures, less common for transmitters |
| Criterion | What to check |
|---|---|
| Class & Division / Zone | Confirm whether the installation uses Division or Zone classification. Both can apply in the same facility. The approval certificate must match. |
| Gas group | Groups A–D for Division system; IIA/IIB/IIC for Zone system. Group B / IIC covers hydrogen — the most stringent. Gas group must match the hazardous substance present. |
| Temperature code | T1–T6 (same as IEC), defining maximum surface temperature. Must be below the auto-ignition temperature of the substance present. |
| Protection concept | IS requires a certified barrier. XP allows more power but is heavier. NI is for Division 2 only. Verify the complete system — transmitter plus barrier parameters. |
| Output signal | 4–20 mA 2-wire is most common for IS installations. HART over 4–20 mA widely available. Verify IS parameters (Vmax, Imax, Pmax, Ci, Li) match the barrier specification. |
| Wetted materials | 316L stainless for general use. Hastelloy C276 for aggressive media. Must match process media compatibility — not just the pressure range. |
| Process connection | 1/2 NPT and 1/4 NPT most common in North America. G-thread variants available for international projects. Flush diaphragm for viscous or particulate media. |
| IP / NEMA rating | NEMA 4X is common for outdoor and corrosive environments. IP67/IP68 for submersible use. Verify the enclosure rating matches the installation environment. |
Division 1 and Class I Zone 1 are similar but not identical. A device approved only for Division 2 cannot be installed in Division 1. Verify the exact Division or Zone marking on the approval certificate.
ATEX is an EU directive and is not recognised as a standalone approval in the US or Canada. FM, CSA or cULus approval is required. Some projects specify both ATEX and FM/CSA — verify what your project specification requires.
For IS installations, the transmitter parameters (Vmax, Imax, Pmax, Ci, Li) must be compatible with the associated IS barrier. This is a system requirement and must be verified before installation.
FM or CSA approval is typically an order option, not standard on every variant. The approval certificate is specific to the device configuration. Verify the configuration you order is within the scope of the certificate.
Verify before specifying: Always confirm the device configuration, approval variant, gas group, temperature code, wetted materials and seal material against the official approval certificate and manufacturer specifications. Pressure Selector provides a shortlist for further evaluation — it does not replace engineering review, certification assessment or approval by the authority having jurisdiction.
For promising matches, use Request Info on any result to prepare a supplier inquiry based on your application requirements.
Pressure Selector converts application requirements — such as FM or CSA approval, Class/Division or Zone classification, gas group, pressure range, output signal, process connection and wetted materials — into a structured shortlist of matching pressure transmitters and sensors.
The results link back to manufacturer specifications and datasheets for verification. Coverage includes selected transmitters, switches and differential pressure devices from manufacturers such as Yokogawa, Endress+Hauser, PMC-STS, Ashcroft, Wika, TE Connectivity and others. Availability of FM, CSA, UL or cULus approval depends on the selected series and device configuration. SIL-assessed variants are available from selected manufacturers.