ABSTRACT
Hydrogen is a highly fl ammable gas and will burn at concentrations as low as 4% in air. The lower explosive limit (LEL) and upper explosive limit (UEL) are the two most common terminologies used to indicate the fl ammable levels for many fuels including hydrogen. As indicated in Table 15.1, hydrogen is one of the least fl ammable materials at 4% but has a larger window (4-75% v/v H2) of fl ammability in comparison to natural gas, gasoline, propane, ethane, methane, propylene, etc. The fl ammability limit of hydrogen is seven times wider than methane (Figure 15.1 [1]). It is, therefore, critical for a hydrogen sensor to have a wider measurement range (1-99% v/v H2) for safety applications than most common fuels. Hydrogen is the lightest of elements and the smallest molecule; it, therefore, has the greatest tendency to leak. Thus, for a process safety application, a hydrogen leak can be more dangerous and its detection becomes more challenging than other gases. This chapter provides a general understanding of different hydrogen sensing technologies, their importance, applications, and limitations. Section 15.2 provides an overview of the hydrogen measuring principles including traditional industrial methods and discusses their limitations. Section 15.3 focuses on the operation mechanisms and recent advancements of low-cost solid-state sensors for hydrogen detection. Section 15.4 outlines the applications of hydrogen sensors in industrial processes. Section 15.5 provides an overview of sensors in hydrogen fuel applications. Section 15.6 provides a brief market overview with a list of manufacturers of hydrogen sensors. The purpose of this chapter is to provide a reference guide on hydrogen sensors for the readers and expert hydrogen community.
