Which of the following describes intrinsically safe equipment?

Intrinsically safe equipment is specifically designed to prevent ignition of flammable materials in hazardous environments. This is achieved by ensuring that the energy levels or temperatures present in the equipment are kept below the thresholds that could cause ignition of explosive gas mixtures.

The concept revolves around controlling the electrical parameters—particularly, energy, voltage, and current—so that any sparks or heat generated during normal operation cannot ignite flammable gases or vapors. Option D accurately captures this essential principle, indicating that the design effectively prevents sparks from being capable of igniting an explosive mixture, which is the fundamental function of intrinsically safe equipment.

The other options, while they specify certain electrical parameters, do not fully encapsulate the critical aspect of preventing ignition in hazardous environments. For example, limits on amperage or voltage alone do not guarantee that a device is intrinsically safe unless they are part of a broader design context aimed at preventing ignition. Therefore, option D conclusively defines what characterizes intrinsically safe equipment.