List each release source and the material it handles, then check that the classified areas drawn around it match the process layout, the materials list, the ventilation, and the electrical equipment selected inside each boundary. AI can flag conflicts; the engineer of record and the authority having jurisdiction decide the classification.
What does NFPA 497 cover?
NFPA 497 is the Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. It is a recommended practice. NFPA’s page states that it presents criteria to determine ignitability hazards in chemical process areas using flammable liquids, gases, or vapors to assist in the selection of electrical systems and equipment for safe use in Class I hazardous (classified) locations.
NFPA’s official NFPA 497 page identifies the 2027 edition as current when checked on October 8, 2026. Confirm the edition, local amendments, and project scope that actually govern the work. The publisher’s newest edition does not establish local adoption.
The wiring and equipment inside a classified area follow the NFPA 70 electrical guide, and the liquids themselves are usually handled under the NFPA 30 guide. Combustible dust classification is a different subject. Because NFPA 497 is a recommended practice, record whether the project, the owner, or the authority uses it as the basis for the classification drawings.
Gather the process data and the classification drawings
Collect the hazardous area classification drawings, the process flow diagrams and equipment list, the materials list or safety data sheets, the process layout with release sources such as pumps, valves, and vents, the mechanical ventilation drawings, the electrical plans and equipment schedules for the classified areas, and the specifications.
Classification drawings are often prepared once and then left behind as equipment moves. Upload the latest process layout with them so each source can be compared with the boundary drawn around it.
Follow each release source to its boundary
| Review question | Sources to compare | Decision to record |
|---|---|---|
| Release sources | Process layout, equipment list, classification drawings | Confirm each pump, vent, or other source on the layout appears on the classification drawings. |
| Materials | Materials list, process flow diagrams, classification notes | Match the material named for each source across the process and classification documents. |
| Boundaries | Classification drawings, plans, sections | Check that classified areas extend to the same walls, floors, and elevations on plans and sections. |
| Ventilation | Mechanical drawings, classification notes, specifications | Ask the engineer to confirm the ventilation the classification relies on is drawn and scheduled. |
| Electrical equipment | Electrical plans, equipment schedules, specifications | Find equipment inside a classified area whose schedule or specification does not reflect the classification. |
| Revisions | Issue dates, revision clouds, equipment list | Identify classification drawings issued before the latest process layout. |
Spray booths and dip tanks bring their own classified areas in the NFPA 33 guide and the NFPA 34 guide. Use the electrical drawing checklist to log the questions, and see manufacturing project review for the plant around them.
Example: a pump moved outside its boundary
Hypothetical example. A process revision relocates a solvent transfer pump to the other side of a room. The process layout shows the new location, while the hazardous area classification drawing still centers the classified area on the old pump position, and a general-purpose motor control panel now sits near the new pump.
The process layout shows the solvent transfer pump in a new location, but the classification drawing still draws the classified area around the earlier position, and the electrical plan places a general-purpose control panel near the new pump. Please confirm the classification and the equipment selected for this area.
The engineer of record revises the classification drawing and the electrical design. The classification and its acceptance remain the engineer’s and the authority’s decisions.
Review hazardous area drawings with Groundbook
Upload the current project PDFs and relevant specifications to Groundbook. Identify the governing issues and add the applicable NFPA 497 reference from a copy you are licensed to use, where the license permits uploading it. State the edition, amendments, review area, and known exclusions in your instructions.
Compare the hazardous area classification drawings with the process flow diagrams, equipment list, materials list, process layout, mechanical ventilation drawings, electrical plans and schedules, and specifications. Flag release sources, materials, boundaries, ventilation, and equipment that differ between sources. Use the supplied NFPA 497 edition where applicable and cite both sources.
Groundbook links each potential finding to the sheets involved and the reference you uploaded.
Document review does not classify areas, calculate extents, or select equipment. Those decisions remain with the engineer of record and the authority having jurisdiction.