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Safety Philosophy

The evaluation of the safety is very important for hydrogen installations as a new technology in general and for hydrogen given its specific hazard features. However since there is no harmonized approach yet on the issue, while various standards and documents are under review and harmonization process yet, the most expected to be adopted approach to the topic is the one considering hydrogen installation as hazardous systems and apply for them risk oriented safety approach, which is currently used for other similar installations. In applying this approach it can be considered that a hydrogen installation is a complex system subject to various challenges, which could induce undesired effects, with various levels of damage impact and hence having various levels of risk. For this approach the main philosophy of reducing the level of risk generated by various hazards to acceptable levels is based on a layer type concept, i.e. considering that the risks are being kept at a low level by using three groups of protection / safety layers.

  • developing a design of the installation, that has inherently safe features
  • implementing in the design of the installation special systems, called safety systems designed to cope with specific challenges
  • developing a set of procedures and managerial approaches to deal with emergency cases, once the previous layers of defense failed.

The safety layers approach is applied for the installation for which a set of groups of challenges (initiating events) are considered. The most representative initiating events for hydrogen installations are as follows:

  • Undetected and/or not vented breaks
  • Undetected and/or not vented leaks
  • Overpressurization
  • Combustion / Fires
  • Low temperatures
  • Hydrogen exposure
  • Hydrogen embrittlement and other passive effects on pipes/components
  • Explosions
  • External events (earthquake, harsh climate, winds etc)
  • Security threats

For each of the above mentioned challenges the installation has to have available features of the three safety layers mentioned above:

  • inherently safe features assuring that the installation will be designed in such manner that it will have a level of protection embedded in the solutions adopted, combined with a prudent operating philosophy, which should try to reach production objectives without endangering the safety level and by performing continuous inspection and maintenance of the installation.
  • safety barriers to decrease the effect of the systems reacting to a set of detection signals on the existing challenges, which will be followed by mitigation functions performed by technical systems
  • mitigation functions and emergency procedures designed as a last layer of protection to decrease the risk on population, environment and workers if all the other layers have failed.

The structure of this chapter illustrates the three layers of protection and their components. This paragraph will mention some generic aspects of the inherently safety features and safety barriers. Inherently safety features are assured by design in order to minimize the severity of the consequences of a certain hazard, which results if the installation is challenges by undesired events. There is a set of strategies adopted for the inherently safe design of hydrogen installations, as follows:

  • The quantity of hydrogen in the system is minimized as much as possible
  • Hydrogen is isolated from substances, which could lead to hazards, as for instance oxidizers, hazardous materials etc. This is assured by various means as for instance by protection walls or other passive systems
  • A set of physical barriers and a zoning concept is adopted in order to separate public or workers from the sources of potential fires, explosions etc in the installation
  • A suitable and highly elevated ventilation system of the hydrogen installation is provided
  • It is assumed that all the compartments and closed spaces of the installation, where there could be potential accumulation of hydrogen, functions of ventilation and/or avoidance of reaching critical volumes of hydrogen and/or contact with hazardous materials are provided
  • The working staff present on a given moment in time in the installation is minimized
  • Operating and maintenance procedures are provided to assure a good level of inspection over the installation
  • Protection by distance and weather condition studies is provided for public and environment in case of undesired events by studying the conditions on the chosen site for the installation and by developing emergency procedures in case of a totally undesired events posing risk to public, environment or workers.

Furthermore for each design adopted the systematic evaluation of the risks and the actions to be taken to keep the risk below the tolerable limits is being performed. This systematic evaluation is called Quantitative Risk Analysis and it is presented in chapter1. Based on the results from the design and operating experience the inherently safety features and preventive actions and functions are provided for the operation of hydrogen installations. They include, but are not limited to:

  • Control of ignition sources
  • Provision of inerting methods and inerting control features
  • Use of recombiners
  • Minimization of possibility for fires and explosions by using adequate electrical equipment
  • Provision of ventilation functions in the installation
  • Development of a comprehensive set of safety procedures for normal and abnormal situations and operating staff training
  • Development of a maintenance plan.
  • Use of verified and validated tools and methods, i.e. computational codes, standards and guides, experimental results etc.

More details on those features are presented in the next paragraphs In case that the first safety layer of the hydrogen installation as described so far fails, than the safety layer of the barriers provided to decrease the risk impact of undesired events is activated.

Safety barriers are activated based on manual / direct human intervention and/or (what is preferable and intended by design) based on the results of detection of dangerous releases and/or accumulation of hydrogen.

There are specific features provided for each installation in order to have a good detection of:

  • hydrogen leaks,
  • hydrogen accumulation in closed spaces,
  • hydrogen flames,
  • hydrogen fire detectors.

More details are included in this chapter at the correspondent paragraph. The mitigation function is assured by a series of mitigation measures, as for instance (which are detailed in the next paragraphs of this chapter):

  • Pressurization of the installation (pipeline or vessel)
  • Explosions of installation followed or not by fires. This can be assured by:
    • providing venting of equipment and buildings
    • explosion suppression and fast acting valves
    • use of maximum experimental safe gap
    • deflagration flame arresters
    • detonation arresters
  • Hazards due to hydrogen interaction with other dangerous substances. This can be assured by
    • hydrogen inerting,
    • hydrogen suppression
    • hydrogen isolation systems,
    • constant inert gas dilution to prevent ignition and combustion
    • Pre-ignition inert gas dilution
    • Water based protection systems
  • Combustion / fires. This can be assured by various measures, as for instance
    • Flame arresters
    • Flame quenching and quenching diameter
  • Hydrogen leaks and hydrogen accumulation in closed spaces
    • Ventilation to mitigate hydrogen accumulation in closed spaces
  • Challenges to the installation due to other sources than hydrogen, i.e. by mitigating flooding, spilling etc of various liquids in the installation
  • Definition of safety distances for various components
  • Emergency response and emergency response plan based on the best results from similar cases and experience as well as based on weather and other environmental conditions simulations, as for instance:
    • Forecast of blast wave propagation and impact force to the protective wall
    • Experimental evaluation and numerical simulation of the damage of surrounding structures by an explosion accident.

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Page last modified on February 23, 2009, at 11:14 PM