Which of the following gases is categorized in Group D?

Group D gases are classified based on their ignition and combustion characteristics, particularly in relation to the minimum ignition energy and the size of the gas particles that can ignite under certain conditions. The key characteristic of Group D gases is their minimum ignition energy (MIE) and the size of the gap through which they can ignite.

Gases with an MESG (Minimum Explosible Spark Gap) above 0.75 mm fall into this category because they are generally less hazardous and have a relatively lower potential for forming explosive mixtures. The MESG is an important metric; it indicates the smallest distance between two electrodes at which a spark can ignite a gas mixture. A higher MESG means that the gas can be ignited only by a larger spark, which contributes to its classification in Group D. This group typically includes gases that present a lower risk of explosion compared to those in other groups.

This classification aids in ensuring safety measures are appropriate for handling and working with these gases, as understanding the ignition properties is critical in fire alarm system design and the broader fire safety context.