Hydrogen Safety Measures

Safety procedures and training

This is probably the most important preventive measure. Such procedures and training are available in the chemical industries using hydrogen. Similar procedures have to be developed for the future hydrogen community.

People handling hydrogen or designing the systems for hydrogen should be familiar with the basic chemical, physical and hazardous properties of hydrogen. They should be also aware of human capabilities and limitations. The training should also address the ignition sources, ignition prevention, materials to be used in a hydrogen system, transport and loading precautions. The system designers should be trained in the accepted standards and codes. The operators should have the knowledge of emergency safety procedures. The trained staff should always be kept informed of any changes in safety procedures.

In addition to the training of professionals who deal with hydrogen, it is also important to train the public, who are going to use the appliances based on hydrogen regarding the basic properties of hydrogen.

Ventilation

Ventilation is useful for preventing the formation of explosive atmospheres when hydrogen is dealt with in confined space. The basic principle of ventilation is to bring fresh outside air inside the room and remove the inside air. The main advantages of using ventilation in hydrogen systems are:

• It prevents the accumulation of explosive gas inside the room.
• It dilutes the explosive gas by bringing fresh air in.
• It limits the resident time of explosive atmospheres.

Ventilation can be of two types, forced (mechanical) and natural. Selection of appropriate type depends on many factors. Natural ventilation functions due to temperature differences, winds and draughts. Hydrogen buoyancy and diffusion characteristics should be taken into account while selection the size of opening and their positions. Although it is cheaper option than the mechanical ventilation, it is less controllable and is affected by weather conditions at the openings. On the other hand mechanical ventilation can give constant and controlled flow. The main concern in mechanical ventilation is the sizing. It can be sized based on the previous experiences, based on calculations or based on hydrogen leak detection sensitivity. The main disadvantage of this type of ventilation is that the gas cloud and air will be more turbulent and in this case if the gas cloud is ignited then the explosions will be more severe. Using a combination of natural and mechanical ventilation can be a solution in some cases.

Automatic shut down system

Inerting

It is defined as the replacement of a sufficient proportion of oxygen contained in a gaseous atmosphere by an inert gas, to avoid the ignition of atmosphere. It is an important way to prevent the formation of explosive atmosphere. However, it can be dangerous for the workers due to the asphyxiating property of inert gas. The main inerting methods include, pressure swing method, volume swing method, flow-through method and displacement method. The inert state of the system should be properly controlled in order to make it safe.

Schematic of Hydrogen-Air-Inert mixtures

The conditions of a hydrogenated atmosphere to be inert can be derived from the triangular diagram representing the hydrogen-air-inert mixtures.

The three coloured zones in the diagram represent:

• Red zone: It corresponds to the explosion area
• Orange zone: It corresponds to the mixtures which are not explosive but which may explode if they are mixed with air. They are relative inert.
• Green zone: It corresponds to mixtures which are not explosive and which will not explode if they are mixed with air. They are absolute inert.

Contents

• 1 Prevention Measures
  • 1.1 Safety procedures and training
  • 1.2 Ventilation
  • 1.3 Automatic shut down system
  • 1.4 Inerting
  • 1.5 Recombiners
  • 1.6 Control of ignition sources
• 2 Detection Measures
  • 2.1 Detection of hydrogen leaks
  • 2.2 Detection of hydrogen flames
• 3 Safety Barriers and Safety Measures
  • 3.1 Mitigation measures
  • 3.2 Explosion venting of equipment and buildings
  • 3.3 Active inerting, suppression and isolation systems
  • 3.4 Water based protection systems
  • 3.5 Passive measures
  • 3.6 Emergency response measures
  • 3.7 Determining the safety distance
• 4 See also
• 5 References