Understanding Hazardous Area Classifications for Flow Meters
When installing flow measurement equipment in oil & gas, chemical, or other industrial facilities, understanding hazardous area classifications is essential. Choosing the wrong equipment rating can create serious safety risks - and choosing an over-rated solution can unnecessarily increase costs.
This guide covers the North American (NEC/CEC) classification system and helps you select the right totalizers, magnetic pickups, and signal cables for your application.
The NEC Classification System
The National Electrical Code (NEC) uses a Class/Division/Group system to categorize hazardous locations:
Class - Type of Hazard
| Class | Hazard Type | Examples |
|---|---|---|
| Class I | Flammable gases or vapors | Oil refineries, gas plants, fuel terminals |
| Class II | Combustible dust | Grain elevators, coal handling, metal powder |
| Class III | Ignitable fibers | Textile mills, woodworking facilities |
For flow measurement in oil & gas, Class I is by far the most common classification.
Division - Likelihood of Hazard
This is where equipment selection really matters:
| Division | When Hazard is Present | Real-World Examples |
|---|---|---|
| Division 1 | Present during normal operations | Inside a tank, at a wellhead, near open vessels, pump seals |
| Division 2 | Only during abnormal conditions | Near flanged connections (leak potential), instrument rooms, pipe galleries |
Group - Specific Gas Type
| Group | Gases | Common In |
|---|---|---|
| Group A | Acetylene | Welding operations |
| Group B | Hydrogen, fuel gases | Refineries, hydrogen systems |
| Group C | Ethylene, cyclopropane | Petrochemical plants |
| Group D | Propane, methane, gasoline vapors, natural gas | Most oil & gas operations |
Most oilfield flow measurement is Class I, Division 1 or 2, Group D.
Protection Methods: Explosion Proof vs Intrinsically Safe
There are two primary ways to make electrical equipment safe for hazardous areas:
Explosion Proof (Ex d)
- How it works: Heavy-duty enclosure contains any internal explosion and prevents it from igniting the surrounding atmosphere
- Suitable for: Class I, Division 1 & 2
- Construction: Cast aluminum or stainless steel with machined flame paths
- Cost: Higher - requires robust enclosures
- Maintenance: Must maintain enclosure integrity; damaged housings compromise safety
Intrinsically Safe (Ex i)
- How it works: Limits electrical energy to levels incapable of causing ignition
- Suitable for: Class I, Division 2 (Division 1 with barriers)
- Construction: Standard enclosures; safety is in the circuit design
- Cost: Lower initial cost
- Advantage: Equipment can be opened for calibration while energized (in Div 2)
Equipment Selection Guide
Totalizers & Flow Computers
| Your Location | Required Rating | Our Solution |
|---|---|---|
| Safe Area (no classification) | General Purpose | EDD-800 (F012) standard |
| Class I, Division 2 | Non-Incendive or IS | EDD-800 (F012) with IS option |
| Class I, Division 1 | Explosion Proof | EDD-E18 (E018) Ex d enclosure |
Magnetic Pickups
Passive magnetic pickups are inherently simple devices. Most are rated for:
- Division 2 applications without special certification (Entity concept)
- Division 1 when paired with an approved IS barrier
Our standard magnetic pickups (4-303, 4-304, 4-5050, etc.) are suitable for Division 2 installations. For Division 1, use with an appropriate IS barrier or contact us for certified options.
Signal Cables
Cable selection matters in hazardous areas:
- Division 2: Standard shielded cable is typically acceptable
- Division 1: Use in conduit or cable rated for the location
- Best Practice: Shielded twisted pair reduces electrical interference
ATEX & IECEx (International Standards)
If you're working internationally or need equipment certified to European standards:
| NEC (North America) | ATEX/IECEx (International) |
|---|---|
| Class I, Division 1 | Zone 0, Zone 1 |
| Class I, Division 2 | Zone 2 |
| Explosion Proof (XP) | Flameproof (Ex d) |
| Intrinsically Safe (IS) | Intrinsically Safe (Ex i) |
Our Fluidwell/EDD totalizers carry ATEX, IECEx, and CSA certifications for global deployment.
Common Mistakes to Avoid
- Assuming "explosion proof" means indestructible - It means the enclosure contains an internal explosion. The device can still fail; it just won't ignite the atmosphere.
- Using Division 1 equipment everywhere - This over-specifies and adds unnecessary cost. Most pipe-mounted flow meters are in Division 2 areas.
- Ignoring temperature ratings - Equipment has T-ratings that must exceed the ignition temperature of gases present. Verify your equipment's T-rating for your specific application.
- Modifying certified equipment - Any modification (drilling holes, changing connectors) voids the hazardous area certification.
- Not consulting area classification drawings - Your facility should have drawings showing exactly where Division 1 and 2 boundaries are. When in doubt, ask your safety engineer.
Need Help Selecting Equipment?
Every installation is different. Our team has decades of experience with flow measurement in oil & gas facilities and can help you select the right equipment for your specific classification.
- Browse our Explosion Proof Electronics
- View all Totalizers & Displays
- Contact us with your area classification and application details
Phone: (432) 214-2045
Email: sales@wagnerflow.com