The EIR3 was housed in a distinctive olive-drab metal case, approximately 2.25 inches wide and 3.25 inches tall. Its operation relied on , a chemical process where specific reactions indicate radiation levels through color changes. Inside the unit, five glass vials contained a mixture of chloroform and stabilizing chemicals, including resorcinol and bromecresol purple dye .
When exposed to gamma radiation, the chloroform in the vials would form an acid. The amount of acid produced was directly proportional to the radiation dose absorbed. This acid caused the purple dye to shift toward a yellow-orange hue. Soldiers could determine their exposure level—ranging from 50 to 450 Roentgens—by comparing the vials against a printed guide on the device. Tactical Importance and Limitations eir3.7z
As a "tactical" device, the EIR3 was designed for high-dose detection in active combat scenarios rather than long-term, low-level monitoring. Its construction was rugged, featuring a belt clip for easy carry and instructions that emphasized shaking the unit before reading it in a vertical position. However, the device had notable vulnerabilities; for instance, users were cautioned against prolonged viewing in direct sunlight to avoid compromising the chemical indicators. The EIR3 was housed in a distinctive olive-drab