Safety-related key figures for explosion protection
According to §3 of the Industrial Safety Ordinance (RL 99/92 / EG), the employer has “the necessary measures in the risk assessment according to § 5 of the Occupational Health and Safety Act, taking into account Annexes 1 to 5, § 7 of the Hazardous Substances Ordinance and the general principles of § 4 of the Occupational Health and Safety Act for the safe provision and use of work equipment. In particular, he shall take into account the hazards associated with the use of the work equipment itself and which are caused in the workplace by the interaction of the work equipment with each other or with agents or the work environment.
“If, according to the provisions of §§ 7 and 12 of the Hazardous Substances Ordinance, the formation of hazardous explosive atmospheres can not be reliably prevented, the employer must judge
- the probability and duration of the occurrence of hazardous explosive atmospheres,
- the likelihood of the presence, activation and activation of ignition sources, including electrostatic discharges; and
- the extent of the expected impact of explosions.”
The resulting explosion protection concepts are based on the explosion triangle from fuel, air and ignition source to break. This is possible with the following principles:
- Primary explosion protection: The occurrence of an explosive mixture is avoided with sufficient certainty, eg by displacement of oxygen from the system.
- Secondary explosion protection: The occurrence of explosive mixtures is permitted. Depending on the probability of the occurrence of such mixtures, requirements are made for the avoidance of effective ignition sources.
- Tertiary explosion protection: The occurrence of explosive mixtures and the simultaneous occurrence of effective ignition sources is permissible. An explosion will take place, but the impact and spread of the explosion will be limited.
Here are the following measures are considered:
- Flameproof design: The system is designed for the maximum explosion overpressure.
- Pressure shock-resistant construction: The system is designed for a reduced maximum explosion overpressure and equipped with pressure relief facilities. A deformation of the plant parts is allowed, but an uncontrolled tearing is not.
- Explosion suppression: active sensors detect the start of an explosion and to stop the reaction, extinguishing agent is introduced into the system.
- Explosion-related decoupling: With active (eg extinguishing device) or passive (eg explosion protection) protection systems, the transmission of an explosion from one part of the system to another is avoided.
These protection principles can be used both individually and in combination to ensure the required protection of the system.
The selected protection concept should, if possible, be chosen so that the operating behavior of the system is not disturbed.
The protection concepts and the associated measures are supplemented both by corresponding regular technical maintenance and also by further organizational measures (eg: maintenance instructions, operating instructions, training of employees)
The selection of the protection principles to be implemented can be carried out, for example, by a systematic risk assessment, eg according to EN 1127-1. The following aspects are to be discussed on the basis of a flowchart from EN 1050:
- Identification of hazards: The explosion risk that emanates from an installation is directly linked to the substances handled in it. The primary issue to be clarified is whether the substances used are explosive or not.
- Evaluate whether explosive mixtures / atmospheres are possible: The probability of the occurrence of explosive mixtures is to be described for the different operating states in a zone classification. In addition to normal operation, the process states to be considered are also the startup and shutdown process as well as frequent and rare malfunctions
- Identify relevant sources of ignition: Depending on the zone classification, the likelihood of effective ignition sources occurring should be assessed. In doing so, frequent and rare errors must be taken into account for the equipment.
- Identification of potential explosion effects: If the simultaneous occurrence of explosive mixtures and effective ignition sources can not be excluded with sufficient certainty, the effects of potential explosions must be limited.
- Assessment of risk reduction measures: The measures envisaged are to be assessed in their entirety and, if necessary, the evaluation must be carried out iteratively.
Often the mistake is made, starting from a possible risk of ignition in one part of the system to install explosion protection for the entire system, which can result in significant expenses. However, it is precisely through a systematic analysis of sources of danger that areas with effective ignition sources can be limited quite precisely. For example, these areas can be separated from other areas by explosion decoupling measures. Here, no constructive explosion protection is required, so that the concept of avoiding ignition sources can continue to be pursued.
For multi-substance plants, eg in the pharmaceutical or plastics industry, the determination of the key figures involves a not inconsiderable expense. Not all key figures are published in the literature and the values determined in standard test procedures depend on the actual process conditions. In addition, the respective key figures must be determined before the use of new substances or substance modifications. However, it is possible to define suitable limit parameters, so that the investigation effort depending on the protection concept is within reasonable limits. Within these limits, new substances can be safely handled in the plants.