Death of a recreational scuba diver during training
On 1 November 2020, PADI Open Water Diver Linnea Rose Mills drowned during a training dive in Lake McDonald in Glacier National Park, Montana, while using an unfamiliar and defective equipment configuration, with excessive weights, no functional dry suit inflation mechanism, and a buoyancy compensator too small to support the weights, which were not configured to be ditched in an emergency. She had never been trained or even given a basic orientation in the use of a dry suit. This defective equipment configuration was supplied by the dive school, and the instructor, who was registered but had not been assessed as competent to train dry suit diving, did not take appropriate action compliant with PADI training standards or general recreational diving best practice, at several stages of the dive.
During the dive, her dry suit was compressed by the ambient pressure, and as she was unable to add gas to restore buoyancy, she became negatively buoyant and was unable to swim upwards, further hindered by suit squeeze. She fell off an underwater ledge while trying to attract the attention of the instructor, and though a fellow diver attempted to stop her descent, he was unable to ditch any of her weights and had to surface to save himself.
The incident was poorly investigated and as of November 2024, no criminal charges have been made, but a civil case for $12 million was eventually settled out of court, and counsel for the plaintiffs has urged the state to prosecute. The Professional Association of Diving Instructors was alleged to have failed in their duty of care by not providing sufficient quality assurance oversight on the dive school and instructor, and by setting standards for training that were ambiguous and in places contradictory, relying on interpretation by the service provider, which allowed plausible deniability of responsibility by PADI if an accident occurred.
Background.
The Missoula dive shop Gull Dive, owned by David and Jeannine Olson, was advertised as a PADI dive school, rented equipment to Mills, and employed the dive instructor responsible for the training.
The dive site, Lake McDonald is a cold freshwater environment, and a dry suit would be standard equipment for the expected conditions. Lake McDonald is the largest lake in Glacier National Park. It is located at in Flathead County in the U.S. state of Montana. Lake McDonald is approximately long, over a mile (1.6 km) wide, and deep, filling a valley formed by a combination of erosion and glacial activity, with steep sides and a relatively flat bottom, requiring good buoyancy control to avoid sinking to excessive depths if overweighted. The surface area of the lake is . Lake McDonald lies at an elevation of and is on the west side of the Continental Divide. Atmospheric pressure at this altitude is approximately 89% of sea level, and this causes gas volume reduction at depth due to hydrostatic pressure to be greater than at sea level, which exacerbates the effects of suit squeeze. Altitude decompression is also affected by the lower surface pressure, and decompression schedules and algorithms must be adjusted to control the risk of decompression sickness. These problems are generally not familiar to divers who have not been trained in altitude diving. 
The diver certification agency, PADI, is the largest recreational diver training agency in the world, and has considerable influence over international minimum training standards by virtue of their overwhelming worldwide market share. PADI training is focused on short, convenient courses, marketed by an emphasis on "fun" and claiming high standards of safety. As of 2020, PADI claims to have issued 28 million scuba certifications of all levels, many of which may be minor specializations. Some of the certifications align with WRSTC and ISO minimum standards, and these are recognized worldwide. Many of the others are not relevant for recognition, as they are unique to PADI and have no equivalence anywhere, or may be part of other agencies' standards for certification for more general diving skill levels, or are not universally accepted as necessary for diver competence or safety. PADI advertises itself as having a strong quality assurance system for members, which include PADI Instructors, PADI Divemasters, and PADI Dive schools, which are contractually obliged to adhere to PADI's standards and pay a significant annual membership fee for the privilege of using the highly recognized PADI name and logo, and for selling PADI training materials and certification. As the training agency, PADI is responsible for ensuring that all certification issued under terms of recognition by international standards agencies, complies with the relevant international standards. PADI is owned by Canadian investment firm "Altas Partners" and French private equity firm "Florac".
The instructor, Debbie Snow, a newly certified PADI Open Water Scuba Instructor, was initially trained as an instructor in Florida in warm sea water but did not pass the evaluation on her first attempt. Two months later she was reevaluated and registered as an instructor with PADI. At this time she was also registered as an instructor for five specialty courses, including Dry Suit Diver by Rainbow Reef, the school she was trained at as an Open Water Instructor, Dry suit diving and altitude diving expose the diver to a set of hazards not generally encountered in entry-level diving as covered by the Open Water Diver course. Such levels of training are generally considered to require specialization training for recreational divers to allow the diver to dive safely and make an informed acceptance of risk. Snow's familiarity with the dive site is unknown.
Snow was assisted by another employee at Gull Dive, Seth Linton (22), whose only diving certification was Junior Open Water Diver, a certification issued to entry level divers between 10 and 14 years old, otherwise equivalent to PADI Open Water Diver. His further experience was not specified, but stated to be hardly greater than that of Mills.
The decedent, Linnea Mills (18), was certified as a PADI Open Water Diver, had a total experience of five dives in warm water and one dive in Lake Seeley, in cold water, in a wetsuit, and had never dived in a dry suit before the incident. She was enrolled on a PADI Advanced Open Water Diver course through Gull Dive, of Missoula.
Mills was wearing a second hand dry suit purchased from a private seller, facilitated by the dive school, because they could not rent a dry suit to a diver who had not been trained in the use of a dry suit. Mills had not used a dry suit before, but she was not given a theory class, a briefing or confined water orientation in dry suit diving before the dive, which would have allowed the selection of appropriate weights and identified any obvious defects or other problems. The dry suit had a relatively uncommon CEJN connector inflation fitting and the scuba diving regulator set rented from the school did not have a compatible dry suit inflation hose connected, so it was not possible to add gas to relieve suit squeeze, or compensate for buoyancy reduction due to suit gas compression at depth. Mills was wearing a small, jacket style buoyancy compensation device (BCD) with a nominal lift capacity of , rented from the school, and diving weights totaling distributed as in the zippered pockets of the dry suit and in the zippered pockets of the BCD, which could therefore not be easily jettisoned in an emergency, also supplied by the school. The watertight zipper of the suit was reported to not close completely and would therefore allow air to escape and water to leak in, and the suit was a poor fit with over-large boots and over-long trouser legs. At the start of the dive, Mills had positive buoyancy with her head out of the water at the surface with an inflated BCD and an unflooded dry suit with unknown buoyancy.
Mills had not filled in a medical statement on enrolling for the course, nor any waiver, liability release, or assumption of risk. The dive school had rented equipment four months earlier to an uncertified diver who subsequently drowned while using it.
Incident.
The group of divers from Gull Dive arrived at Lake MacDonald at about 4 p.m. as daylight was fading. Two additional students who had completed dry suit training were already waiting there. While preparing for the dive, the instructor's assistant discovered that the regulator's low pressure hose fitting was incompatible with Mills' dry suit, and notified the instructor, who told Mills to use the BCD for buoyancy control during the dive.
Use of the BCD is standard practice for general buoyancy control, but the absence of an inflator hose makes it impossible to relieve suit squeeze and retain basic suit buoyancy.
Mills was given of loose dive weights instead of the standard quick-release weight belt or integrated weight pockets for the BCD, which were loaded into the dry suit (20 lb) and BCD zipper pockets (24 lb). None of the weights were visible or easily jettisoned in an emergency by Mills or by another diver. It is not known who put the weights in the suit's pockets.
No on-site dive briefing was given, and Mills was not assigned a dive buddy, which would normally imply that the instructor would personally monitor the student throughout the dive, and the group entered the water at about 5 p.m., a short time before sunset. They descended to about and after about 5 minutes, one diver was cold and needed to surface. The instructor escorted the cold diver out of the water, leaving Mills without professional supervision or a properly allocated buddy. After returning to the group, the instructor and assistant took Mills and Bob Gentry to . Gentry was carrying an action camera on a frame with two video lights, which recorded much of the activity of the dive.
At , the dry suit was significantly compressed by the ambient pressure of 1.8 atm above surface atmospheric pressure of about 0.89 atm. The air in the suit was compressed to less than 1/3 of the volume at the surface, and suit buoyancy had decreased in proportion. Mills was standing on a ledge, unable to swim upward due to insufficient buoyancy, and was unable to attract Snow's attention when she swam past with her attention apparently fixed on the compass in her hand. Mills then signaled to Gentry, the diver with the GoPro, who approached her to assist, but she fell backwards off the ledge and began sinking. Gentry eventually caught up with her at a depth of , where suit squeeze would be making it relatively difficult for her to move.
Gentry attempted to find and release Mills' weights but could not find them, and tried to provide her with air from his secondary demand valve when she dropped her demand valve. An effort by Gentry to lift Mills and swim her up by finning hard failed and Gentry left her as his own air was running low. He made a rapid ascent to the surface from in less than a minute, putting himself at a raised risk of decompression illness. When he reached the surface, he was alone, but Snow surfaced after an undisclosed period. Gentry informed Snow of the emergency and she dived to look for Mills, but failed to find her. On a second search dive, by Snow and Liston, Mills was found at , a depth significantly greater than the limit set by PADI for Open Water Diver certification. Liston then made a rapid ascent to the surface and Mills was recovered to the surface by Snow, after ditching the scuba set with the weights in the BCD pockets.
Snow and Liston were airlifted to Seattle, Washington, "for treatment for potential injuries", since Liston had been complaining of effects of his rapid ascent and had used up the available emergency oxygen. Consequently, they were not on site when the initial investigators and coroner arrived.
Several other irregularities and alleged breaches of PADI procedure and general recreational diving safety procedure were cited in the complaint lodged for civil action, some of which may have had a material influence on the outcome of the dive. Others were more relevant to non-compliance with PADI standards by Gull Dive and Snow.
Investigation.
The initial investigation was conducted by local park agents who consulted a range of diving specialists, but it was soon taken over by National Park Service