Hazardous Areas Classification on Ship (Examples and explanation by Rules)

It’s will be a long and confusing contents through all the requirement from IEC/IECEx as well as IMO (SOLAS, IBC, IGC codes). Thus, i’ll make it as short as possible to make the article with key knowledge & understanding.

Note: It used for Marine/Offshore project.


Hazardous area classification in respect of selection of electrical equipment, cables and wiring and positioning of openings and air intakes.

“Hazardous areas are defined as areas in which a flammable or explosive gas and air mixtures is, or may normally be expected to be, present in quantities such as to require special precautions for the construction and use of electrical equipment and machinery.” – IEC 60092-502



“Areas where flammable or explosive gases, vapors, or dust are normally present or likely to be present are known as hazardous areas. Hazardous areas are however more specifically defined for certain machinery installations, storage spaces and cargo spaces that present such hazard, e.g.:

Helicopter refueling facilities, see 4-8-4/27.3.3;

Paint stores, see 4-8-4/27.3.3;

Cargo oil tanks and other spaces of oil carriers; see 5-1-7/31.5;

Ro-Ro cargo spaces; see 5-10-4/3.9.2.”


FLASH POINT of a material is the Material’s Temperature making it ready for Explosion by ignition.
Gasoline = – 45°C
Diesel fuel = + 55°C
* High flash point liquids are less hazardous than low flash point liquids.
* Practically liquids with flash point above 55°C are not liable to generate a hazardous area, unless they are likely to be submitted to a temperature above this flash point.


Hazardous areas are classified into 3 zones based upon the frequency of the occurrence and duration of an explosive gas atmosphere, as follows:

Zone 0
Area in which an explosive gas atmosphere is present continuously or for long periods or frequently.


Ex: The interiors of cargo tanks, slop tanks, any pipework of pressure-relief or other venting systems for cargo and slop tanks, pipes and equipment containing the cargo or developing flammable gases or vapors.

Zone 1
Area in which an explosive gas atmosphere is in which an explosive gas atmosphere is likely to occur in normal likely to occur in normal operation operation occasionally occasionally.

Note: Paint store also cassified as Zone 2 as IEC 60092-502

Ex: Any spaces adjacent to integral cargo tanks ( void, cofferdam, pump room ). Area within 3 m of any cargo tank outlet, gas or vapour outlet or within 1.5 m of cargo pump room entrances, cargo pump room ventilation inlet, openings into cofferdams or other Zone 1 spaces or  up to a height of 2.4 m above the deck or 3 m beyond the manifold. Vertical cylinder of unlimited height and 6 m radius cantered upon the center of the outlet.


Zone 2
Area in which an explosive gas atmosphere is not likely to occur in normal operation but, if it does occur, will persist will persist for a short period for a short period only.

Ex: Area within 10 m horizontally from any cargo tank outlet or gas or vapour outlet. Areas within 1.5 m surrounding open or semi-enclosed spaces of zone 1. Spaces 4 m beyond the cylinder of zone 1.


Non hazardous area (safe area )

A non hazardous area is an area in which an explosive atmosphere is not expected to be present


  • Electric items:

Electric equipment:  To be certified intrinsically-safe Ex(ia)-Zone 0/ Ex(ib)-Zone 1

Electric cable: Electrical cables are not to be installed in hazardous areas except as specifically permitted or when associated with intrinsically safe circuits. ( Mean not All cables passing through Hazardous zone to be I.S certified, but the I.S system/equipment.

  • Hull/Hull outfitting items:

ABS – Pt 5A: Where structural members pass through the boundary of a tank, leakage into theadjacent space could be hazardous or undesirable, and full penetration welding is to
be adopted for the members for at least 150mm on each side of the boundary.

ABS – Pt 4 Cable trays and protective casings passing through hazardous areas are to be electrically conductive.

ABS -Pt 5C: An inspection tank (observation tank) is to be provided for detection of oil contamination in the condensate return. The tank is to be of the closed type, dedicated to the cargo heating system only, with no interconnection to any other system, and vented to the weather. The vent outlet is to be fitted with a corrosion resistant flame screen. The inspection tank may be located within the machinery space, in which case, the vent is to terminate outside of the cargo area and the area within 3 m (10 ft) of the outlet is to be considered hazardous



• The compartment arrangements shall be provided with separation from the hazardous
space by two gas tight self-closing doors without hold back arrangements forming an airlock capable of maintaining an overpressure.
• All ventilation inlets and outlets are routed such that they are located outside of the hazardous area.
• The relative overpressure or air flow is to be continuously monitored and so arranged that in the event of a ventilation failure (loss of relative overpressure or loss of air flow) an audible and visual alarm is given at a manned control station and the electrical supply of all equipment (not necessarily of the certified safe type) is to be automatically disconnected.
• The mechanical ventilation system is to have at least twenty (20) air changes an hour or as required by the BWMS manufacturer, whichever is greater, that will maintain the separate compartment under a positive pressure relative to the external hazardous area.

  • Piping items:

ABS -Pt 5C: Bulkhead penetrations of gas sampling pipes between safe and hazardous areas are to be of approved types and have the same fire integrity as the division penetrated. An isolation valve is to be fitted in each of the sampling lines at the bulkhead on the safe side. 


Regardless of the fluid being conveyed, plastic piping is to be electrically conductive if the piping passes through a hazardous area. – ABS – Part 4

In order to prevent dangerous build-up of static charges resulting from the flow of fluid in piping, the following items are to be earthed (grounded) to the hull such that the resistance between any point on the piping and the hull (across joints, pipe to hull) does not exceed 1 MΩ:
• Piping and independent tanks containing fluids having flash point of 60°C (140°F) or less.
• Piping that is routed through hazardous areas.

BV-Part C: The ballast water treatment system, if intended to be fitted in locations where flammable atmospheres may be present, is to comply with the relevant safety regulations for such spaces. Any electrical equipment of the system is to be located in a non-hazardous area, or is to be certified as safe for use in a hazardous area. Any moving parts, which are fitted in hazardous areas, are to be arranged so as to avoid the formation of static electricity.

Note the pipe penetration between hazardous and safe areas.

“Tanks and spaces separated from cargo tanks by a single deck or bulkhead may be contaminated by cargo oil or vapor due to possible impairment of the common boundary. These tanks and spaces are therefore, in principle, to be regarded as hazardous spaces. Piping serving or having an opening into these tanks or spaces is likewise to be regarded as contaminated” ABS SVR 5C.1.7 -1.7.2 Spaces Adjacent to Cargo Tanks (2012)


By using special designate, the hazardous air will be stop to come in Safe zone.

Hope it’s quite enough for general concept during your surveys on Hazardous area.

About the confusion between each code (IMO, IEC, IBC, IGC) refer to this file

Comparision between code

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