Oil Tanker Safety Design And Hazardous Area Classification

Oil tanker are ships specialized in carrying bulk liquids, and the cargoes mainly refer to the transportation of bulk crude oil and petroleum products with flash points of 60°C and below. According to IEC-60092-502, ships transporting oil products with flash point below 60°C have higher danger, and the specification has more detailed requirements for the division of hazardous area, and all electrical equipment in the hazardous area should meet the relevant explosion-proof requirements. The hazardous area classification of oil tanker is a very important part of their safety design.

Principles of Hazardous Area Classification for Oil Tanker

The classification of hazardous areas for oil tanker is mainly in accordance with IEC-60092-502 for liquid cargo ships carrying flammable liquids with a flash point of not more than 60°C. It divides the hazardous areas into: Zone 0, Zone 1 and Zone 2, with Zone 0 being the most hazardous and Zone 2 the least. Cargo holds, oil and water tanks, any pressure vacuum piping or other ventilating systems in the same area as the cargo holds, and internal spaces containing cargo or piping and equipment handling flammable gases or vapors are all classified as Zone 0. 

The definition of Zone 1 is relatively complex and consists of the following: a) enclosed premises immediately adjacent to the liquid cargo tanks; b) compartments where cargo hoses are stored as well as enclosed and semi-enclosed premises containing cargo lines; and c) areas adjacent to hatchways, gas or vapor outlets, cargo dispensing valves, cargo pipe flanges, and pressure and vacuum valves in the liquid cargo tanks. 2 can be simply understood as an extension of Zone 1, e.g., Zone 1 premises, entrances, exits, and ventilation and air openings. The outward extension of Zone 1 at the boundary of the open deck area, such as entrances and exits, ventilation and air vents. In addition, according to the characteristics of the open deck structure, the cargo hold area with "turned out" bone material up to a height of 2.4 meters above the deck is considered Zone 1, and the deck with "turned out" bone material up to a height of 2.4 meters above the deck is considered Zone 2.

Layout and Impact of Various Types of Openings

The openings of oil tanker are mainly divided into the following three kinds: first, the openings for personnel access and daily use, such as manhole covers, hatch covers, doors, windows and wash hatch covers; second, the cabin ventilation, such as natural ventilation, mechanical ventilation, positive pressure ventilation; third, the breathable system, such as air tubes, bathymetry tubes, high-pressure relief valves, breathable masts and vacuum releasers. The first type of opening needs to meet the crew's requirements for use and pay due attention to the impact of hazardous areas, and the discussion here focuses on the arrangement and impact of hatch ventilation and special breathable systems.

Reasonable and effective ventilation can prevent the accumulation of combustible gases, usually in the form of intake air and extract air. For the ventilation of dangerous places, firstly, it should be far away from the ventilation of safe places; secondly, the air inlet of dangerous places should be in the safe area as far as possible, if it is really unavoidable, it is necessary to consult with the classification society in time; lastly, the air outlet can not be arranged in the more dangerous area, otherwise the danger level should be increased. Taking the ventilation arrangement of pump compartment of an oil tanker as an example, the pump compartment is adjacent to the cargo oil tank of 1 area, due to the factors of personnel operation, this area is not an inert area, so the ventilation environment of the pump compartment is extra important. Pump compartment is in the way of pumping (30 times / hour) for ventilation, pump compartment air inlet and outlet should be as far away as possible from other sources of danger, and the two can not affect each other. The air inlet must be in a safe area, but according to the specification, 3 meters around the air inlet of the pump chamber is also a hazardous area, which must be taken into account in the design.

High-pressure venting valves, venting masts and vacuum releasers in cargo holds are venting devices specific to oil tanker. These devices release oil and gas into the outside air when the pressure of the oil and gas in the cargo hold is too high, and therefore the IEC has also given the strictest limits to the hazardous areas of such devices. The area around the liquid cargo breather pipe which provides a large amount of gas or vapor mixture generated during cargo handling, ballast or expulsion of gas from the liquid cargo tank, the vertical cylinder of unlimited height with a radius of 6 meters upward from the breather pipe, and the open deck area within a hemisphere with a radius of 6 meters downward from the breather pipe, or the semi-enclosed area of the open deck, belong to Zone 1, and the 4 meters outside of Zone 1 belong to Zone 2, as shown in Fig.  Simply put, their sphere of influence is a cylinder with a radius of 10 meters and an unlimited height. The positioning of the cargo hold ventilators should take into account the following factors: first, keep away from the superstructure; second, avoid the ventilation of the deck storeroom in the cargo hold section and the deck searchlight mast; third, keep a distance of at least 10 meters from the door of the Bowman's storeroom.

Conclude

For the design of oil tanker, explosion-proof is an important part of the safety design, if the design is not proper, it will lay great danger for the future use. Designers should pay attention to the classification of hazardous areas of the oil tanker, and pay attention to the coordination of various parties in the design process, so that all kinds of openings, ventilation, air and cabin layout of the oil tanker can meet the regulations and norms. Qinhai constantly improves its internal management level, emphasizing on quality front control and process management.We have obtained CCS quality management certificate issued by China Classification Society,and passed the certification and environmental impact assessment and acceptance by government departments.In recent years, the company complies with the national strategic deployment and the requirements of informationization and intelligent development of ship industry.Promote the "integration of the two" and continue to implement production automation and intelligent manufacturing.We have several automatic assembly and semi-automatic  production lines.