Tank Safety

Considering the various types of tanks and the hazards surrounding them, safety and matters related to the passive defense of tanks in industry are inevitable, and examining such matters at the time of design, construction, startup, operation, repair, and maintenance is of great importance. In order to raise the level of safety, matters such as fire, fluid pressure, corrosion, overflow, etc., must be addressed with greater seriousness. Every factory or company, for storing materials as well as stockpiling or warehousing its various products, needs a large number of tanks. Reasons for using tanks 1- Storing raw materials and unit feedstock 2- Storing intermediate materials 3- Storing products (finished goods) 4- Storing materials for loading, distribution, and dispatch 5- Homogenizing the quality of the product 6- A criterion for measuring the volume of feedstock and produced product Important parameters in selecting the type of tank In general, there is no comprehensive and uniform classification for storage tanks. The classification of tanks can be made from different viewpoints such as geometric shape, type of fluid, or the vapor-pressure label of the substance stored in it, but all tanks can be divided into two general categories: open tanks and closed tanks. Gases, flammable fluids, dangerous chemicals such as acids or bases, and fluids that emit toxic vapors must be kept and stored in closed tanks. Among closed tanks one can mention fixed-roof tanks, floating-roof tanks, spherical tanks, cylindrical tanks, and cold tanks. Open tanks are one of the simplest forms of tanks and are in the form of a wall without a roof. Pits are one of the simplest open tanks, which are dug into the ground and made from inexpensive materials. Of course, not every type of ground can be used to build this kind of tank, and clay soil is often used because of its high impermeability. These tanks, due to the lack of a roof and the contact of the fluid with the outside environment, are usable for storing materials with the following conditions: 1- Their volatility is very low; because high volatility causes evaporation and loss of the substance. 2- They are non-flammable. 3- They are not expensive materials; because there is a possibility of the material being contaminated, unless the purity of the fluid is not important or there is the possibility of treatment before use. Since different materials have different chemical and physical properties, the conditions and the way of storing them differ from one another. For this reason, selecting the suitable type of tank is of great importance. The most important parameters in selecting the type of tank include the following: a) Volatility, or in other words the vapor pressure of the fluid b) Toxicity of the fluid c) Flammability of the fluid Types of hazards in tanks The tank itself is recognized as a potential source of injury and damage in various industries, which can lead to irreparable damage and disasters. Generally, the types of hazards surrounding tanks are: 1- The substance 2- Height 3- Electricity 4- Static electricity 5- Weather conditions Fire in tanks In many oil-storage tanks there is the possibility of a fire. The warming of the air, an increase in tank temperature, the creation of static electricity, the blowing of wind in dry weather, and the failure of people to observe safety principles can cause such a fire; therefore, alongside this type of tank, firefighting equipment must be used, because a group of these tanks are placed next to one another. Explosion in tanks Many accidents involving explosions in the vapor space of fixed-roof tanks have occurred continuously. According to 1997 reports, in Canada alone 25 to 30 explosions related to storage tanks occurred. The reason for the large number of explosions is the presence of mixed vapors in relation to storage tanks. Among the other causes of explosion is the pressure inside the tank, which can be prevented by selecting a suitable wall and also suitable safety equipment such as safety valves. It is almost impossible to be certain of the absence of a spark factor, especially if the fluid inside the tank has low electrical conductivity, in which case static electric charges accumulate in the fluid medium and can increase the likelihood of explosion. For this reason, for many companies a permit for forming flammable materials is not issued. In a factory, the production of products is carried out continuously. But because sales are often periodic, it is necessary for products to be stored and made ready for sale. It should be noted that the contents of one tank may be the product of the work of hundreds of people over a period of several weeks, and the smallest carelessness and error in relation to these tanks can bring about great economic losses. Therefore, to you, dear readers, it is recommended that, by obtaining the book "Tank Safety: Strategies and Predictions of Passive Defense", a work by Mr. Arash Ghasemi, engineer, Dr. Alireza Nariman Nejad, and Mr. Mani Abdollahzadeh, engineer, you gain complete and comprehensive information about this important and vital subject in industry, so that we can have a small share in observing safety principles and reducing the hazards arising from them in the industry of our dear country, Iran.