Group B gases are characterized by which factor?

Group B gases are characterized by a Maximum Experimental Safe Gap (MESG) value that is less than or equal to 0.45 mm. This specification indicates the ability of a gas to propagate a flame in the presence of a gap. A lower MESG signifies that the gas has a higher propensity for flame propagation and presents a greater risk in terms of explosion or fire hazards in industrial environments.

Understanding the MESG value is crucial for safety when working with various gases, especially in the context of fire alarm systems and hazardous locations. Group B gases, which are often more flammable and can present more significant risks in terms of ignition, require careful consideration in design and installation of fire suppression and alarm systems.

The other options relate to different characteristics or classifications of gases, but the defining attribute of Group B is specifically tied to the MESG value.