ENGINEERING EXPLAINED / ZONE
The zone map is a separate calculation.
Explore hazardous-area definitions, ignition-protection principles and the difference between stored energy and an ignition spark.
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01 / CLASSIFIED AREAS
Frequency, not a danger score.
The coloured shapes are conceptual examples, not a site classification drawing or concentric distance rules. A zone describes how often an explosive gas atmosphere is present. Extents depend on release grade, rate, gas properties, ventilation and the actual layout.
Some parts of a chemical site are unclassified; some areas in vehicle manufacturing, including paint operations, can be classified. The comparison in the reel concerns an unclassified assembly area, not every building in the automotive industry.
02 / TWO PROTECTION PRINCIPLES
Contain ignition.
Or limit the circuit energy.
Ordinary phones, motors, batteries and radios cannot simply be assumed suitable for a classified location. Certified equipment must match the zone or equipment protection level, gas group, temperature class and installation requirements. Intrinsic safety applies to an assessed system and its faults, not merely a small battery.
03 / HOW SMALL IS A SPARK?
Hydrogen can ignite at about 0.02 mJ.
That minimum applies near a readily ignitable hydrogen–air mixture under stated test conditions. Composition, pressure, temperature and the discharge affect ignition.
E = ½CV²
This is an illustrative capacitance and voltage calculation, not a measurement of a person. Not all stored energy necessarily couples into an incendive spark. A robot battery's total stored energy is also not the energy of a particular spark; protection must consider available fault energy and ignition mechanisms.
04 / VENTILATION HELPS; CLASSIFICATION NEEDS MORE
A dilution thought experiment.
This assumes a perfectly mixed steady enclosure: gas volume fraction ≈ release / (release + ventilation). It neither assigns zones nor predicts safe distances, local plumes, ignition likelihood or ventilation reliability. Do not use it to classify an installation.
- HSE: hazardous area classification and ignition-source control.
- HSE: zone definitions.
- US DOE-hosted hydrogen safety reference: about 0.02 mJ minimum ignition energy in air.