Is hydrogen flammable, and if so, at what percentage in air?

Hydrogen is indeed flammable, and the correct range for its flammability in air is between 4% and 75%. This means that when hydrogen is present in air in concentrations within this percentage range, it has the potential to ignite and burn.

The lower explosive limit (LEL) of hydrogen is around 4%, signifying that if its concentration drops below this point, it will not ignite. Conversely, the upper explosive limit (UEL) is approximately 75%, indicating that concentrations higher than this are too rich to ignite. This broad range reflects the high flammability of hydrogen, making it a significant safety concern in environments where it is present.

Understanding these properties is crucial, especially when handling or working with hydrogen as part of gas-related applications, ensuring that appropriate safety measures are implemented to mitigate fire hazards.