During which condition is the usage of fog horns most critical?

The usage of fog horns is most critical during conditions of low visibility. This is because fog horns are specifically designed to alert other vessels to your presence when the ability to see other ships or navigational markers is severely limited. Low visibility can result from fog, heavy rain, or other weather phenomena that obscure vision, making it difficult for mariners to determine their surroundings. In these situations, the sound emitted by fog horns serves as a vital navigational aid, allowing others to hear nearby vessels and avoid potential collisions.

In contrast, while fog horns might still be heard in clear weather and can be used at night, the primary purpose of such signals is to enhance safety during conditions where visibility is compromised, making low visibility the most critical scenario for their use. Similarly, although fog horns may have relevance during heavy rainfall, low visibility encompasses a broader range of situations where safety is particularly at risk. Nighttime navigation can also pose challenges, but again, the immediate need for fog horns is tied closely to the amount of visible light and clarity, which is significantly diminished in low visibility scenarios.