Submerged Operations/Operating Limits
The range of environmental and submersible limits within which
Alvin may be safely operated has been developed. These
limits, listed below, are not to be exceeded except in the case
of a properly approved, preplanned mission or in case of emergency
to ensure the safety of personnel.
- The Pilot-in-Command will have the authority to terminate
a dive by whatever means necessary at any time that he feels
a hazard to the submersible or personnel exists, without
regard to mission success or completion
- Alvin will not be operated in an area where water
depth exceeds 5,000 meters.
- Alvin will not be operated below a depth of 4,450
- Alvin will not be operated in such a fashion so
as to pass under any object, either natural or man made.
- Alvin will remain clear of wreckage, debris, or
natural terrain features which have entanglement or entrapment
- Alvin will remain clear of any explosive devices
which may be sighted.
- Alvin will not operate without an effective means for obstacle avoidance and for detecting the existence of hazards in the immediate area.
An attempt is made to ensure that all equipment on Alvin
and Atlantis is operational whenever the submersible
dives. Certain equipment on both vessels has no effect on operational
safety; it is left to the discretion of the Expedition Leader
and the Chief Scientist as to which, and how much, of this equipment
may be out of operation without posing a threat to the scientific
success of the dive. Certain other equipment, particularly that
for life support and communications, is considered vital and
must be operational any time that Alvin submerges. Loss
of this equipment during the dive may or may not constitute
a reason for aborting the dive, depending on whether adequate
backup is immediately available.
There must be a clearly defined need for the dive, normally involving scientific, engineering, or training objectives. Weather predictions for the next 24-hour period must be favorable. Agreement must be reached among the Chief Scientist, the Expedition Leader, the ship’s Master and the designated pilot that there is a reasonable probability of a successful launch, dive, and recovery. Any one of these four persons can veto the decision to dive. The probability of a successful launch and/or recovery is low when the wind is above 25 knots or the sea state is higher than 4 (6 to 8 foot waves). Night operations are not precluded, but they entail increased personnel and operational hazards and thus require optimal weather conditions. If a particular science requirement calls for night dives, advance notice should be given to allow proper planning.
Working Near Moorings and Cables
There are situations where users may request that Alvin
work near moorings and cables. The following two Alvin
operating limitations (see above) help determine if the submersible
can safely work near a particular mooring or cable: 1) Alvin
will not be operated in such a fashion so as to pass under
any object, and 2) Alvin will remain clear of objects
which have entanglement or entrapment potential.
In the case of a mooring (defined here as a flexible tension member anchored to the bottom and connected to a passive floatation package), Alvin will work near the mooring taking into consideration prevailing currents in order to avoid a location under the estimated horizontal displacement of the array. Refer to the implodable volume limitations described in the Scientific Equipment Interfaces: Pressure Housings section for a determination of how close the submersible may approach mooring components.
Due to surface dynamics and cyclic cable loading, cables leading to a ship or equivalent (as opposed to a passive floatation package) are treated as a separate case. Alvin will maintain a horizontal distance from the ship of at least the length of any overboard cable.
Note: Those programs that deploy moorings or do wire work in areas of repeated scientific interest should be aware that lost cabled equipment that is not recovered may preclude future Alvin operations in that area due to the resultant entanglement hazard.
These requirements may become more restrictive if, in the opinion of the Expedition Leader or ship's Captain, the immediate circumstances of the proposed work would pose a risk to the submersible or others involved in the operation.
Daily Dive Planning
Early on the day preceding a scheduled dive day, the Chief Scientist is required to inform the Expedition Leader of the total weight of the observers and equipment allotted to the next day’s dive. This information allows the pilot, at the end of the current day's dive, to fill the variable ballast tanks with the appropriate amount of water to counterbalance the weight expected on the next day's dive. Also, preparation for installation of allotted equipment can begin with adequate time to resolve implementation problems.
Every observer is given a briefing inside the submersible before
making his or her first dive. This briefing, which takes about
30 minutes, details the locations of observer controls and instruments
and covers normal and emergency procedures, including the donning
of emergency breathing equipment. See Appendix
E for an example of the briefing checklist which must be
completed and signed by observers before diving.
In addition, the Alvin Operations Manual should be reviewed by each observer before his or her first dive. It contains detailed descriptions of normal and emergency operating procedures, vehicle performance data, casualty procedures, and other information. A copy is located in the personnel sphere for reference during an emergency if necessary.
Prior to the start of each dive, the Chief Scientist will be asked to sign the final page of the predive check off sheets. These forms are filled out by the Alvin crew during their routine safety and operational checks on the vehicle and must be inspected and signed by the pilot, Surface Controller, Expedition Leader, support ship Master, and Chief Scientist before the dive may take place. This practice is intended to be an important part of the Alvin safety assurance process, but it loses much of its effectiveness unless the Chief Scientist, like the other signatories, takes the time to review the check sheets carefully. Each sheet provides an indication of normal submersible conditions. If the entries are not initialed, if the values recorded do not fall within the limits specified, or if equipment needed is not fully operational, the Chief Scientist should request an explanation from the Expedition Leader. Before signing, he should ensure that all sheets have been completed and that he has been informed of the reasons for and consequences of all discrepancies.
As a complex machine, Alvin requires one extensive maintenance period every two to three years in order to ensure proper operation and the safety of personnel. In the past, this overhaul has been conducted during the winter months at Woods Hole, when the weather in New England waters was unsuitable for diving operations. Now that operations in remote parts of the world are possible aboard Atlantis, and voyages lasting two years or longer have become the norm, most general maintenance of Alvin will be done away from Woods Hole and even the major overhauls may be done in distant ports.
SCUBA Diving Regulations
All SCUBA diving under the auspices of the Woods Hole Oceanographic
Institution (i.e., aboard WHOI vessels, see Diving Section)
must be approved in advance by the Diving Safety Officer (DSO)
or Diving Control Board (DCB). A Dive Plan form is available
from the DSO and must be filed in advance by the designated
shipboard Dive Master. Occasionally, limited diving operations
for the purpose of observing or filming Alvin launch
procedures have been approved by the DSO upon receipt of a written
request including the names of dive team members and a synopsis
of their diving experience and certification status, plus a
brief statement of the purpose and procedures of the dive. For
these dives, a certified WHOI diver is normally required to
accompany the non-WHOI divers with the responsibility of ensuring
that submersible launch operational personnel are fully aware
of the location and status of the divers at all times.
The Master of the vessel is responsible for all diving operations conducted from the ship and has the authority to terminate all diving operations if, in his judgement, conditions endanger the vessel or personnel. A safety boat is required for dives away from the ship, and the boat operator shall be continuously aware of all diver locations. If divers are tethered, precautions shall be taken to avoid entanglement, umbilical buoying, etc. Diving in the vicinity of Alvin, or when an Alvin dive is in progress, also requires the approval of the Expedition Leader.