BYKHY Hazard Zones for Liquids: Articles 116 and 117

The Turkish Fire Protection Regulation (BYKHY) splits places where flammable vapour can form an explosive mixture into three hazard zones (Article 116) and limits the equipment allowed in each (Article 117). The zone dimensions, however, are scattered across the articles on warehouses, open tanks, underground tanks, filling points and fuel stations. This article collects the definitions, the restrictions and every dimension in one place.

Three zones: definitions (Article 116)

Article 116 defines the zones "subject to compliance with the relevant regulations and standards". The BYKHY dimensions below are therefore a minimum framework within the fire regulation; they do not replace the detailed area classification required for the site by legislation on explosive atmospheres.

What may be used in each zone? (Article 117)

The Zone 2 limit of "4/5 of the ignition temperature" is a surface-temperature rule: a luminaire, motor casing or heater must stay well below the auto-ignition temperature of the vapour present. The text does not state the temperature scale; applying the fraction in degrees Celsius gives the lower, safer limit.

The December 2024 Guide adds two notes (pp. 191–192): underground and aboveground storage tanks, road tanker compartments and their fittings should comply with the relevant standards and be certified; and at fuel stations, explosion-protected systems, vapour recovery and earthing should be used at the dispensing point and while filling underground tanks.

Zone dimensions: the scattered clauses in one table

The Guide draws these zones in Figures 116, 118.4 and 119.4 (pp. 191, 193, 198).

The logic behind the numbers

• 0.8 m height recurs almost everywhere. Flammable liquid vapours are usually heavier than air and spread near the ground, so the zones are wide and shallow.
• 5 m radius is the basic value for warehouse openings, tank shells and discharge openings.
• The filling point gets the largest zone: 15 m of Zone 1. Vapour is pushed out continuously while filling, so a mixture is expected in normal operation.
• In a bund, Zone 1 fills the bund: vapour can pool behind the wall, so the bund volume up to 0.8 m above its top edge is Zone 1.

Design consequences

• Electrical installation: every luminaire, socket, motor and junction box inside Zone 1 must be explosion-protected. As the whole store room is Zone 1, warehouse lighting falls under this rule; Article 118(9) also requires mechanical ventilation to be explosion-protected.
• Layout: a facade, parking bay or transformer inside the 15 m filling zone may need relocating at design stage.
• Vehicle access: vehicles enter Zone 1 only with measures that prevent an explosive mixture (117(1)(b)); plan the tanker unloading area with this in mind.
• Gas cylinders: in Zone 2, compressed and liquefied gas cylinders may only stand in a 120-minute enclosure (117(1)(c)).

Common mistakes

• Thinking of zones only around tanks. The area outside warehouse doors and windows is Zone 2 for 5 m.
• Forgetting the vent outlet. The area round the vent opened during discharge is Zone 2; an underground tank's vent pipe must discharge to open air at least 4 m above ground (120(2)(ğ)).
• Applying the gas cylinder rule to extinguishers. Article 117(1)(c) exempts extinguishers explicitly.

Related detail: warehouses, aboveground tanks, underground tanks and filling points, fuel stations.

Frequently Asked Questions

What equipment may be used in Zone 1 under BYKHY?

Article 117(1)(b) allows only explosion-protected, spark-free equipment and systems in Zone 1. Vehicles may enter only where measures prevent an explosive mixture forming.

Is the area outside a flammable liquid store a hazard zone?

Yes. Under Article 118(4) the store room is Zone 1, and a 5 m radius from its doors, windows and other openings to the outside is Zone 2 up to 0.8 m above the floor.

How large is the hazard zone at a tanker filling point?

Article 120(4)(c) makes a 15 m radius around the filling point up to 0.8 m above ground, plus a 5 m radius around the fill opening up to 3 m above it, Zone 1.

Is there a surface temperature limit in Zone 2?

Article 117(1)(c) allows only equipment that does not spark and does not reach 4/5 of the ignition temperature of the vapour-air mixture.

What is the hazard zone around a fuel dispenser?

Under Article 121(3) the inside of the dispenser is Zone 1 and a 1 m radius from its centre, up to its height, is Zone 2.

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