Chapter 4
Hazardous area classification and zones
Published
- Hazardous area zones explained: Zone 0, Zone 1 and Zone 2
Zone 0, 1 and 2 describe how likely an explosive gas atmosphere is and how long it lasts. Definitions, the often quoted hour guidance, typical examples, EPL and ATEX category mapping and a worked tank example.
- How to carry out a gas hazardous area classification step by step (IEC 60079-10-1)
A practical ten-step method for gas hazardous area classification under IEC 60079-10-1: data, substances, sources and grades of release, release rate, ventilation, zone type, extent, documentation and review, with a worked example.
- Grades of release: continuous, primary and secondary
Continuous, primary and secondary grades of release explained: definitions from IEC 60079-10-1, examples for vents, sample points, seals and flanges, how grades lead to zones, and how to handle sources with more than one grade.
- Ventilation in area classification: degree of dilution and availability
How IEC 60079-10-1 uses ventilation: natural and artificial ventilation, high, medium and low dilution, good, fair and poor availability, and how they combine with the grade of release to set the zone type, with an indoor example.
- Estimating the extent of a hazardous zone: release rates and dilution
How far does a hazardous zone reach? Hole sizes, release rate equations for gas, liquid and two-phase leaks, the release characteristic, the IEC 60079-10-1 charts, EI 15 and API RP 505, with a worked natural gas example.
- The Explosion Protection Document (EPD) and area classification drawings under ATEX 1999/92/EC
What the Explosion Protection Document required by Article 8 of ATEX 1999/92/EC must show, how it links to the risk assessment, what goes on area classification drawings, who is responsible and when the EPD must be revised.
- Zones vs Divisions: IEC and ATEX zones compared with NEC Class I Division 1 and 2
Division 1 roughly equals Zone 0 plus Zone 1, and Division 2 roughly equals Zone 2, but groups, temperature codes and equipment rules do not map one to one. NEC Articles 500, 505 and 506 compared with IEC and ATEX zones, with tables and pitfalls.
- Typical hazardous area examples: tank vents, pumps, compressors and loading points
Typical zones around fixed-roof tanks and vents, pumps, compressors and road tanker loading, how EI 15, API RP 505 and prescriptive tables describe them, a worked US example with distances, and why every case still needs a site-specific check.
- Battery rooms and charging areas: hydrogen ventilation and hazardous areas
Charging lead-acid and NiCd batteries splits water into hydrogen and oxygen. How the IEC/EN 62485-2 ventilation formula works, a worked example, the safety distance around cell vents, when a zone is needed and why lithium-ion rooms are different.
- Laboratories, workshops and small quantities: when is a hazardous area needed?
Small quantities of solvents and gases do not automatically need hazardous zones, but the decision must be justified. Zone NE, the 10 litre rule, fume cupboards, solvent cabinets, aerosol cans and a practical approach for labs and workshops.
- Pressurised rooms and analyser houses: making an area non-hazardous by ventilation
How IEC 60079-13 protects rooms in hazardous areas: pressurisation pb and pc at 25 Pa, artificial ventilation vc, purging with 10 room volumes, door rules, gas detection at 25 % of the limiting value, alarms and analyser houses, with a worked example.