Colors and Appearance
According to EN/IEC 60947-5-5, EN/IEC 60204-1, and EN ISO 13850, buttons used as actuators of an emergency stop device shall be colored red. When a background exists behind the actuator, and as far as it is practicable, it shall be colored yellow. Most suppliers of push buttons accomplish the yellow background in one of three ways: 1. Use of a yellow enclosure. 2. Use of a large Emergency Stop legend that is yellow. 3. Coloring the “stem” of the push button yellow. Note: Use of a yellow guard is also accepted in some industries, though this is not typically allowed. This will be discussed in more detail later in the paper. NFPA 79 has the same aforementioned color requirements, but takes it a step further stating: “The RED/YELLOW color combination shall be reserved exclusively for emergency stop applications.” NFPA 79 also requires the actuator be a mushroom-head or palm type. The mushroom-head shape is also a requirement of EN/IEC 60204-1 and EN ISO 13850. Mushroomhead means that the top of the button must be extended and rounded like the top of a mushroom. Traditionally, European emergency stop push buttons are actually shaped like a cone with a rounded top (Figure 1), while in North America emergency stops are shaped more like a traditional mushroom (Figure 2). The perceived advantage of the cone shape is that if an object is hung on the stem of the push button, the cone may lift the object out of the way and still operate.