Chemical, pharmaceutical, manufacturing and other process industries are characterised by a constant increase of technological complexity and diversity of products. The presence of hazardous materials in reactors, pipelines and reservoirs at high temperatures and pressures has greatly increased.
The industrial development in the 20th century led to the increase of the amount of transported energy in processes, the size of plants has increased by 10 times, plants contain huge compressors and distillation columns, large quantities of chemicals are transported by various means of transport, plants are interconnected and exchange substances, the amount of raw materials, products and intermediates (an intermediate is a substance that is produced and consumed in or used in a chemical process in order to be transformed into another substance) in processes has increased. These factors increase the risk and make hazard control more difficult, leading to accidents in plants caused by defects in material (e.g. due to corrosion) or errors in operation, such as an increase in temperature or pressure over the critical value.
In the chemical industry, safety has always received a lot of attention and the number of fatal accidents does not exceed those in other branches of industry. However, major disasters repeatedly emphasize the need to carefully, thoroughly and systematically address the field of security.
The accidents in Flixbourough, UK, where cyclohexane exploded in 1974, and in Seveso, Italy, where TCDD (tetrachlorodibenzo-p-dioxin) was released in 1976, played an important role in the development of the field of safety and loss prevention. Another accident which echoed strongly in the public was the disaster in Bhopal, India, where in 1984 over 2000 people died as a result of poisoning with methyl isocyanate, while more than 200,000 were injured.
To prevent such unwanted events or at least reduce their frequency, the developed countries have been trying to raise the level of safety in the process industry through sound management of safety policies and the planning and preparation for dealing with accidents. Today, the only way to ensure efficient hazard control is by means of a systematic approach, efficient organization, regulations, standards, legislation and experts. It is important to establish where the potential hazards can occur, as the only dangers that can be studied and prepared for are the ones that we know. Some even say that a known danger is no longer a danger.
Process industries include plants that produce or process inorganic and organic chemicals, oil, natural gas, pharmaceuticals, soap, oils, grease, rubber, paper, plastics, synthetic fibres, industrial gases and waste-water treatment plants. The chemical industry is therefore one of the branches of the process industry.
Most process industry plants process gases and liquids, while some also process solids in the form of powder, sludge or suspensions. In such plants, the process equipment consists mainly of closed vessels interconnected by piping through which the fluids whose flow is regulated by valves flow. Process equipment also includes tanks or fluid reservoirs.
Process equipment in the chemical industry is often referred to as process units, for example, a reactor, a mixer, a distillation column, a compressor, a pump, a heat exchanger, etc. The process units and their interconnections are shown graphically in the form of a process flow diagram.
The substances found in the processing industry plants have very different properties. Some are completely harmless, others highly flammable, explosive, highly reactive, toxic, asphyxiating, or corrosive. These substances are treated or processed at very different operating conditions, such as at vacuum or at very high pressure and in a wide temperature range from almost the absolute zero to up to 2000 °C and more. The rapid economic development often leads to the increase of production volume (“scale up”) in the process industry plants. The capacity of the plants for the production of sulphuric acid, for example, in the last fifty years increased from 10 t to 1000 t daily, which represents a hundredfold increase. The increase of the volume of production leads to the increased levels of hazardous substances in processes, which is the main cause of danger in process industries.