Abstract: An assembly is disposed on a helmet for monitoring predetermined thresholds of ambient thermal condition of the helmet. Such assembly includes at least one thermistor for sensing the status of an ambient thermal condition and a signal comparator for detecting each predetermined threshold. Individual LED's visually indicate when each predetermined threshold is reached, while an audible alarm indicates when a hazardous predetermined threshold is reached. The audible alarm is further utilized to indicate if the battery voltage is under a predetermined threshold which is predicated on the breakdown voltage of a reference diode when a test switch is closed. A temperature responsive switch is also included to conserve the life of the battery by activating and deactivating the assembly about a predetermined temperature level.

Abstract: There is disclosed a pressure monitoring device for self-containing breathing apparatus including visual indicators disposed in the field of view from the headpiece to monitor when predetermine pressure levels are reached in the tank which supplies gas to that headpiece. The predetermined pressure levels are referenced to the residual tank pressure at which the required breathing gas flow is not sustained and visual alarm provisions anticipate those predetermined pressure levels which are critical, in some embodiments of the invention. A cost effective transducer of reduced pressure range senses the tank pressure and noise is eliminated from the transducer signal by common mode rejection in still other embodiments.