During in-water decompression sickness (DCS), what is the first step to take?

In the scenario of in-water decompression sickness (DCS), the priority is to ensure the safety and well-being of the diver experiencing symptoms. The first step in addressing DCS is to launch standby to assist. This is vital as immediate support is needed to monitor the diver's condition and provide assistance, whether that means helping them to ascend or providing first aid as necessary.

Having a standby diver ready is crucial for several reasons. Firstly, DCS can present with symptoms that may rapidly worsen, and having assistance on hand ensures that a trained person can respond quickly. Secondly, the situation may require quick evacuation from the water or adjustment of the dive profile, which can be efficiently managed with another trained individual present.

The other options may not effectively address the immediate needs of the affected diver. For instance, descending further or continuing to the next scheduled stop could exacerbate the condition, while switching to a higher concentration of oxygen is an important follow-up step but should not replace the need for immediate assistance. Having standby personnel ready to assist will provide the necessary support to respond appropriately to the situation, making it the correct first action to take.