The primary and most obvious difference between work performed by divers and work performed by topside personnel is the environment in which tasks are conducted.  

Specific impacts on the underwater environment – such as weather, contamination, crane or tugging operations, stray electrical current in the work area, vessels using active SONAR in the vicinity, and equipment that may become energized while the diver is in the water – often are overlooked by those unfamiliar with commercial diving. 

The following environmental variables affecting dive conditions must be considered:

• Current can often become too strong for a diver to operate effectively.  If the current results from tidal action, the dive should be scheduled during periods of slack tide.
• Other issues relating to the tide must be considered during marine projects, in addition to tide-induced current.  For a variety of reasons, some work can be accomplished most effectively at either high or low tide, which impacts scheduling.  Also, a rising tide during a long dive may force a change in a decompression table, which must be taken into account during each day’s pre-dive safety meeting.
• Visibility, or lack of, may limit some operations, but divers frequently ply their trade in black water.  Where a record must be made in such limited-visibility situations, infrared cameras can be employed.
• Sea state can have a significant impact on divers, especially if dive operations are conducted from a vessel that is subject to such wave action.  Importantly, in-water decompression in rough seas may be impossible if the diver would likely be pulled away from the scheduled in-water decompression stop.  Such a scenario is dangerous and to be avoided at all costs.
• Vessel traffic in the area can likewise be a concern, both because some vessels produce an enormous wake and because many vessels are operated by irresponsible individuals who motor too fast or too close to the dive platform.
• Vessel Movement must be considered in dive operations conducted from a moving vessel (so-called “live boating”).  Such operations are inherently more dangerous and carry with them additional safety precautions.  Even when not live boating, however, vessel movement must be taken into account in the dive plan.  Take for example the situation where a diver enters the water during flood tide to perform work on a vessel moored alongside a pier.  When the tide turns, the positioning of the vessel may likewise change.  The change in position can be quite dangerous if not anticipated in the dive plan.
• Differential pressure (Delta P) situations often exist, for example at hydroelectric dams and beneath vessels with a ruptured hull.  It is of paramount importance to either eliminate the differential pressure prior to the diver entering the water or to account for the Delta-P situation in the dive plan.

Divers must ascertain which conditions can be addressed by altering the dive plan and which conditions can (and should) be avoided altogether. 

During project planning, experienced commercial diving companies conduct an effective hazard analysis and present the available options to their clients in an understandable way.