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Free course · Intermediate · 4 h 18 min · v1.0

Hazardous Locations (HazLoc) Basics

Class, Division, Group and temperature code — 29 CFR 1910.307 and 1910.399, free and self-paced

Start the courseSee the outline
This course is an optional step of the Industrial Mechanic — Learning Path — take it when the work calls for it.
Not OSHA-authorized training. This free course is a study aid. It does not satisfy any OSHA or regulatory training requirement and no certificate or card is issued. Your employer's training program comes first.

A hazardous location is not a place where something dangerous is stored. It is a place where the air itself may become fuel, and where an ordinary light switch is an ignition source. This free, self-paced course explains the American system for those places: what has to be present for an area to be classified, what Class I, II and III mean, how Divisions 1 and 2 and the Zone alternative describe how often the fuel is there, why equipment is marked with a group and a temperature code, and what keeps an installation safe long after the electrician has gone home. Every requirement is quoted with the paragraph it comes from.

What you will be able to do

  • Explain what has to be present for an area to be a hazardous (classified) location, and name the three ingredients of a fire and the two more that make a dust explosion
  • Tell a Class I, a Class II and a Class III location apart, and say what Division 1 and Division 2 describe
  • Read the nine designations of 29 CFR 1910.307(a)(2)(i), and say why construction under 1926.407 has only six
  • Explain what a gas group and a temperature code are for, and where the value for your own material and your own equipment comes from
  • Read the class, group and temperature marking on a piece of equipment and say what it is approved for
  • Recognize the field conditions — an open enclosure, a missing bolt, an unsealed conduit, a dust accumulation — that quietly cancel the protection a classified installation was built with

Course outline

Part 1

Why hazardous locations exist

What has to be present before an area needs classifying: fuel that can reach an ignitable concentration, an ignition source, and — for dust — dispersion and confinement.

  1. 1.1 What makes an area hazardous (classified)14 min
  2. 1.2 Gases, vapors and the flammable range13 min
  3. 1.3 Combustible dust and the explosion pentagon15 min
  4. 1.4 Ignition sources: what the equipment brings, what people bring14 min
  5. Part 1 quiz5 questions
Part 2

Class, Division and Zone

The classification system itself: what is present decides the Class, how often it is present decides the Division or the Zone, and each room is judged on its own.

  1. 2.1 The logic of the system, and the nine designations13 min
  2. 2.2 Class I: flammable gases and vapors15 min
  3. 2.3 Class II dust and Class III fibers and flyings15 min
  4. 2.4 The zone system, and why construction does not have it14 min
  5. Part 2 quiz5 questions
Part 3

Groups, temperature and what is stamped on the equipment

Why the class alone is not enough, what a gas group and a temperature code are for, how to read a nameplate, and what each protection technique physically does.

  1. 3.1 Why groups exist, and where the values live14 min
  2. 3.2 Temperature classification: the surface is the ignition source14 min
  3. 3.3 Reading the nameplate, and what "approved" means15 min
  4. 3.4 The protection techniques, and what each one actually does14 min
  5. Part 3 quiz5 questions
Part 4

Keeping it that way in the field

A classified installation is only as good as its last repair: enclosure integrity, documentation, work permits, housekeeping, and knowing where your job stops.

  1. 4.1 Enclosure and conduit integrity: the protection you can undo with a screwdriver14 min
  2. 4.2 Documentation, drawings and what changes a classification13 min
  3. 4.3 Working in a classified area: permits, testing and housekeeping15 min
  4. 4.4 Where your job stops, and who does the rest14 min
  5. Part 4 quiz5 questions
Final exam
20 questions · about 20 minutes
Go to the exam

Who it's for: Maintenance technicians, electricians and instrument techs, plant and facility operators, EHS staff, and contractors who work in refineries, chemical plants, paint booths, grain elevators, woodworking shops, spray finishing areas and fuel handling facilities.

Frequently asked questions

No. Area classification is engineering work performed with the material's properties, the process, the ventilation and the building in front of you. For the zone system, 29 CFR 1910.307(g)(4)(i) requires that classification of areas and selection of equipment and wiring methods be done under the supervision of a qualified registered professional engineer. This course teaches you to read and respect a classification somebody else made.

No. Nothing is issued. SteelToeTools is not affiliated with, endorsed by or authorized by OSHA or the U.S. Department of Labor, and this free content does not satisfy any regulatory training requirement. Only OSHA-authorized trainers deliver OSHA Outreach Training and issue DOL cards.

Because the groups are defined in NFPA 70, the National Electrical Code, which is a copyrighted consensus standard. OSHA itself points to it: the note to 29 CFR 1910.307(c)(2)(i) says NFPA 70 lists or defines hazardous gases, vapors and dusts by groups. The course explains what a group is for and where you find the one that applies to your material — the safety data sheet, the classification study for your plant, and the marking on the equipment.

No. It is about the OSHA standards that govern electrical safety in classified areas — 29 CFR 1910.307 and 1910.399 for general industry, 1926.407 and 1926.449 for construction — and about the physical reasons behind them. OSHA references NFPA 70 for equipment design and for the group definitions, and this course tells you when you have crossed that line and need the code itself.

Not usually. A location is classified on the likelihood that ignitable concentrations are present, not on a measurement taken today. Division 1 covers places where they may exist under normal operating conditions; Division 2 covers places where the material is normally confined and would only escape through an accident or an abnormal condition. That is the whole point of the system: the equipment has to be right before anything goes wrong.

Yes, in a slightly shorter form. 29 CFR 1926.407 covers the same ground for construction, with definitions in 1926.449, but it assigns six designations rather than nine — the Class I zone system of 1910.307(g) has no construction counterpart. Part 2 of this course puts the two side by side.

Not on its own say-so. The classification belongs to the area as designed and documented, and changing it is a decision, not an observation. 29 CFR 1910.307(b) requires areas classified under the Class and Zone system, and areas classified under the Class and Division system after August 13, 2007, to be properly documented, and that documentation to be available to those authorized to design, install, inspect, maintain or operate equipment there.

In Class II, and it is the part people miss most. OSHA's SHIB 07-31-2005 describes the explosion pentagon — fuel, ignition, oxygen, plus dispersion and confinement — and the primary explosion that shakes loose settled dust and feeds a far more destructive secondary explosion. Part 1, Chapter 3 works through four investigated incidents in which exactly that happened.

Sources & references

Content checked against these sources — last reviewed September 1, 2026.

Not OSHA-authorized training. SteelToeTools is not affiliated with, endorsed by, or authorized by OSHA or the U.S. Department of Labor. This free educational content does not satisfy any OSHA or other regulatory training requirement, and no card, certificate, or credential is issued. Only OSHA-authorized trainers can deliver OSHA Outreach Training (10-Hour and 30-Hour) and issue DOL cards. Always follow your employer's training program and applicable federal, state, and local requirements.

By — Editorial team of SteelToeTools.com (published by LSEA SAS) Updated v1.0