In general:
The term "safety" should only ever be used within the meaning of preventing a risk primarily to people and not within the meaning of the reliability of a system (cf. operating safety). This does not preclude the fact that some safety measures also serve to increase reliability (Figure S 55).
In this context, in accordance with DIN 31 004 "Safety is a situation, in which the residual risk of a failure is smaller than the tolerable risk".
In the case of technical processes, there is no absolute safety. To minimise the residual risk, determinations in terms of safety technology are made, namely: "special information on technical values and measures, compliance with which – in the interaction with other technical measures –– should ensure that by keeping within the tolerable risk, the safety objectives are met at the operating conditions to be expected.
In addition to these general safety determinations, there are a series of safety regulations in the form of laws and legislation, which the manufacturer or importer of a system has to consider if he wants to avoid being held liable in the case of damage.
The safe use of fluid-based systems is primarily the responsibility of the system designer. He must design the system so that all regulations are followed. However, the operator must also take all necessary safety measures and strictly comply with his obligations in terms of the regulations.
In hydraulic systems:
Due to the compressibility of the medium in connection with the high pressure, this means that large quantities of energy are stored. The sudden release of this compression energy may be very dangerous for plant operators. This is particularly true if hydraulic accumulatorsare also used. There are also risks in connection with overloading.
Therefore, the specific safety principles outlined in DIN 24 346 demand that the devices are selected, mounted and the pipes are laid such that
- risks which arise when hydraulic fluids are released (these grow alongside the hydraulic capacity),
- risks based on unintentional machine movements and
- risks based on forces above the permitted level.
In controls:
The safety requirements placed on controls state as follows:
- They must not endanger, harm or unnecessarily inconvenience someone,
- they must be protected against external influences, which may cause malfunctions,
- the impact of wear and ageing on safety must be taken into consideration.
To meet these requirements, the circuit connection of the individual elements must also be correct. In addition to preventing switching errors, e.g. in the case of electrical actuation, this includes the fact that in the case of a power failure, there must be no risk for the personnel, including the installation of redundant elements, fault detection procedures (diagnostics) and the creation of non-hazardous fail safe positions.
Figure S 55: Safety and availability of a system