In the case of fuel-rich mixtures like those in the question, the heat of combustion for the mixture should be calculated on the basis of the oxygen content of the mixture. The heat of combustion per mole oxygen is twice the heat of combustion per mole hydrogen, i.e., it is 286*2 kJ per mole O2. You should be able to do the calculations based on this reply.

Regarding the concept of introducing hydrogen gas into natural gas pipelines, this is indeed a hot topic and there are recent quantitative treatments of fatigue crack growth driven by pressure cycling and potentially accelerated by hydrogen.  Some analysis has shown that it can be acceptable to operate natural gas pipelines with a hydrogen blend.  However, this is highly dependent…

Hydrogen cylinders contain pure hydrogen unless they are specifically manufactured for and marked as a mixture. The purity grade is usually between 99.5% and 99.9999%. The balance is typically inert gases (such as nitrogen) with just ppm levels of other contaminants, but this can vary depending upon the production source. When emptied, the residual is still the same purity of hydrogen, just at…

It is possible to store large quantities of gaseous hydrogen above ground, but it will likely require a large footprint due to its relatively low density even at high pressure. Also, if the quantity equals or exceeds 10,000 lb., the facility will need to comply with OSHA 1910.119 process safety management requirements if located in the US. Similar regulations exist in Europe and Asia that…

This production rate of hydrogen of about 96 kg/h is quite significant, which depending upon the application might require a significant amount of storage. There will be a need to determine how many kg the project wants to store from this production rate in order to determine how much hydrogen ground storage is needed. Since the project is in Europe, look for pressure vessel manufacturers that…

This can be a complex problem and response to insulation failure should be considered in the emergency response guidelines and procedures. 
First, a tank with an insulation failure may boil off at an elevated rate which applicable codes build into the relief device and vent system design.
Second, ice and oxygen enriched liquefied air can form where inadequately insulated surfaces…

This is not an easy question since many factors influence how much hydrogen can be transferred from one vessel at a higher pressure to another one at a lower pressure and the rate at which it can be transferred. The pressure in the higher vessel will fall while that in the lower vessel will rise as gas is transferred, so the flow rate will typically slow down and eventually stop as the…

It varies slightly due to different density of LH2 at different temperatures, but a gallon of LH2 at atmospheric pressure (0 psig) is ~113 SCF of H2. The expansion ratio is about 840:1. In metric units, a liter of LH2 at atmospheric pressure (0 MPa) would expand to about 840 liters of STP of gaseous pressure.

The National Fire Protection Association (NFPA), the Compressed Gas Association (CGA), and the Society of Fire Protection Engineers (SFPE)   represent the U.S. fire protection and engineering community, and these organizations publish handbooks and standards/guidelines that describe the properties of hydrogen. There are many other organizations and documents that provide similar…

This is an impossible question to answer without greater understanding of the quantities of hydrogen involved, the types of vessels involved, and the atmospheric conditions. Several companies offer software to model such releases. It’s important to note that there is a high probability of ignition either during the vessel rupture or from nearby ignition sources.