Which of the following methods requires a chlorine compound strength of over 25 ppm?

The fogging method requires a chlorine compound strength of over 25 ppm because it is used to disinfect large and open spaces where even distribution of the disinfectant is critical. This method creates a fog or aerosol of chlorine solution, allowing it to reach surfaces that may be difficult to access otherwise. The higher concentration ensures that the chlorine effectively kills pathogens in the air and on surfaces, which is particularly important in settings such as food processing facilities where sanitation is a priority.

In contrast, other methods such as immersion, paste, and flowing methods utilize different application techniques where the chlorine concentration may not need to be as high. Immersion techniques involve soaking items in a chlorine solution, where the concentration can be adjusted based on the volume of water and surface exposure. Paste methods typically involve applying a stronger mixture directly to specific surfaces, while flowing methods use a continuous stream of water mixed with chlorine to maintain cleanliness without the necessity of a higher ppm level that fogging demands.