Aggie Safety experts provide explosion protection electrical classification support for hazards associated with flammable atmospheres in a facility, including explosion likelihood assessment, hazard controls, and electrical classification requirements.
| Standard / Directive | Specific Standards / Description / Notes | Links |
|---|---|---|
| OSHA (1910.307 – Hazardous (classified) locations) | Code of Federal Regulations | 1910.307 – Hazardous (classified) locations. | Occupational Safety and Health Administration |
| RAGAGEPs like NFPA standards | NFPA 68, 69, 70, 77, 654, 484, 61 | Codes and standards | NFPA |
| ATEX Directives | 2014/34/EU and 1999/92/EC where applicable | Guidelines to Directive 2014/34 EU – ATEX 'Product' Directive | Safety and health at work EU-OSHA |
| IEC/EN 60079 series | Explosive Atmospheres | Standards | IECEx |
| Local fire codes, Fire Marshall Directives, Building Codes and insurance requirements | Need compliance to run a business in a county and meet local authority requirements |
Use your local county Fire Marshal contact. Example: Harris County: Harris County Fire Marshal's Office |
Presence of Explosion atmospheres in the plant
A formal risk assessment shall be conducted to:
Safety teams must document all assessment results and reviewed periodically or upon process change.
Avoidance of Explosive Atmospheres
Avoidance of Ignition Sources
| Zone | How Often Explosive Gas Atmosphere Exists | Typical Locations | Risk Level |
|---|---|---|---|
| Zone 0 | Present continuously or for long periods | Inside tanks, fuel storage vessels, reactor interiors | Highest |
| Zone 1 | Likely during normal operation | Around pump seals, valve flanges, sampling points | Medium |
| Zone 2 | Not likely in normal operation, and if it occurs, only briefly | Areas adjacent to Zone 1; well-ventilated spaces where leaks are rare |
| Zone | How Often Explosive Gas Atmosphere Exists | Typical Locations | Risk Level |
|---|---|---|---|
| Zone 20 | Present continuously or for long periods | Inside tanks, fuel storage vessels, reactor interiors | Highest |
| Zone 21 | Likely during normal operation | Around pump seals, valve flanges, sampling points | Medium |
This table summarizes hazardous (classified) location definitions commonly used in North America under the National Electrical Code (NEC) Class/Division system (Article 500). Always confirm the applicable code edition and authority having jurisdiction (AHJ) requirements for your site.
| Classification | Hazard Type | Definition |
|---|---|---|
| Ordinary / Unclassified | Not classified | No hazard is expected from flammable gases/vapors, combustible dusts, or ignitable fibers/flyings in quantities sufficient to produce an ignitable atmosphere under normal or abnormal conditions. |
| Class I, Division 1 | Gases / vapors | Ignitable concentrations of flammable gases or vapors can exist under normal operating conditions, or may exist frequently because of repair/maintenance or leakage, or because of equipment/process that can release the hazard during normal operation. |
| Class I, Division 2 | Gases / vapors | Flammable gases or vapors are normally confined in closed systems/containers and would be present in ignitable concentrations only under abnormal conditions (e.g., accidental rupture, breakdown, or unusual equipment failure). |
| Class II, Division 1 | Combustible dust | Combustible dust is (or may be) in suspension in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures, or mechanical failure/abnormal operation could produce such mixtures and provide an ignition source. |
| Class II, Division 2 | Combustible dust | Combustible dust is not normally in suspension in ignitable concentrations, and dust accumulations are normally insufficient to interfere with equipment heat dissipation; dust may be present due to abnormal conditions. |
| Class III, Division 1 | Fibers / flyings | Ignitable fibers/flyings are handled, manufactured, or used under normal operating conditions. |
| Class III, Division 2 | Fibers / flyings | Ignitable fibers/flyings are stored or handled but are not likely to be in the air in a way that produces ignitable mixtures under normal operation. |
These apply where combustible dust (grain, sugar, flour, aluminum, plastic, coal, etc.) can form explosive clouds.
Note: Examples above are representative (not exhaustive). Group selection depends on the actual gas/vapor or dust characteristics at the site (including ignition properties), and the final classification is determined by the authority having jurisdiction (AHJ) and applicable code edition.
| Class | Group | Typical Materials / Examples |
|---|---|---|
| Class I | A | Acetylene |
| Class I | B | Hydrogen; manufactured gas |
| Class I | C | Ethylene; ether; cyclopropane |
| Class I | D | Propane; gasoline vapors; butane; alcohols; natural gas |
| Class II | E | Metal dusts (e.g., aluminum, magnesium and their commercial alloys) |
| Class II | F | Carbonaceous dusts (e.g., carbon black, charcoal, coal/coke dust) |
| Class II | G | Grain and other combustible dusts (e.g., flour, starch, grain dust, plastic dust, chemicals) |
T-codes (temperature codes) specify the maximum surface temperature that equipment is permitted to reach. To be acceptable, the equipment’s marked T-code must be below the autoignition temperature of the gas/vapor or dust present (and within the equipment’s marked ambient temperature range, if shown).
Note: Examples above are representative (not exhaustive). Group selection depends on the actual gas/vapor or dust characteristics at the site (including ignition properties), and the final classification is determined by the authority having jurisdiction (AHJ) and applicable code edition.
| T-Code | Max Surface Temp (°C) | Max Surface Temp (°F) | T-Code | Max Surface Temp (°C) | Max Surface Temp (°F) |
|---|---|---|---|---|---|
| T1 | 450°C | 842°F | T3A | 180°C | 356°F |
| T2 | 300°C | 572°F | T3B | 165°C | 329°F |
| T2A | 280°C | 536°F | T3C | 160°C | 320°F |
| T2B | 260°C | 500°F | T4 | 135°C | 275°F |
| T2C | 230°C | 446°F | T4A | 120°C | 248°F |
| T2D | 215°C | 419°F | T5 | 100°C | 212°F |
| T3 | 200°C | 392°F | T6 | 85°C | 185°F |
| T-Code | Max Surface Temp (°C) |
Max Surface Temp (°F) |
|---|---|---|
| T1 | 450°C | 842°F |
| T2 | 300°C | 572°F |
| T2A | 280°C | 536°F |
| T2B | 260°C | 500°F |
| T2C | 230°C | 446°F |
| T2D | 215°C | 419°F |
| T3 | 200°C | 392°F |
| T3A | 180°C | 356°F |
| T3B | 165°C | 329°F |
| T3C | 160°C | 320°F |
| T4 | 135°C | 275°F |
| T4A | 120°C | 248°F |
| T5 | 100°C | 212°F |
| T6 | 85°C | 185°F |
Selection reminder: Equipment markings must match the Class/Division (or Zone) and Group and have an appropriate T-code. For dust locations, the nameplate may show a temperature in °C (e.g., T135°C) rather than a T-code.
