What Does End of Service Life Indicator (ESLI) Mean?
An end of service life indicator (ESLI) is a system used for breathing apparatuses to alert the wearer that the oxygen or air level is reaching its lower limits. In some cases, the indicator will also provide information about potential damage to the apparatus. A color change typically notifies the wearer before the contaminant breaks into the cartridge and becomes hazardous to that worker's health.
Safeopedia Explains End of Service Life Indicator (ESLI)
Breathing apparatuses are equipped with end of service life indicators to indicate when the filtering capacity of the apparatus has reached its limit. The ESLI may be a feature built into the apparatus, but it may also refer to traits that show that an apparatus is damaged in some way. In a self-contained breathing apparatus the indicator works in the form of alarm. The alarm tells the wearer that he or she is running short of breathable air and should evacuate immediately.