In case of lost visibility due to suspended particulate matter, a diver should take which step first?

In situations where visibility is lost due to suspended particulate matter, the primary step a diver should take is to establish and maintain contact with the guideline. The guideline is a vital safety feature in underwater navigation, particularly in low-visibility environments. It serves as a tactile reference point, allowing the diver to orient themselves and safely navigate back to the entrance or exit of the cavern.

By following the guideline, a diver significantly reduces the risk of disorientation and potential hazards that come with swimming blindly in dark or murky waters. The guideline provides a clear path and can help prevent the diver from becoming lost in an environment where spatial orientation is compromised.

Other responses, while they might seem relevant, do not prioritize maintaining safety and orientation in the water as effectively as keeping in contact with the guideline. Swirling sediments can obscure a diver's visibility, making it easy to lose track of direction, so focusing on the guideline is the most effective first action in such scenarios.