S N MacKinnon, E Bradbury Massey and L Petrie, Memorial University of Newfoundland, Canada A Simoởs Rộ and A Akinturk, Institute for Ocean Technology, National Research Council, Canada J Boone, Marine Institute, Memorial University of Newfoundland, Canada
SUMMARY
Life rafts are widely employed by maritime vessels around the world as a means of evacuation during emergency situations. While operators typically demonstrate due diligence in training their employees in standard operating procedures, these are generally completed under benign environmental conditions. The purpose of this study was to examine performance of several life raft management tasks under calm and controlled wave conditions.
There was a 2 hour training session delivered by survival training experts to all subjects prior to the data collection sessions. During the training session the following tasks were demonstrated: tying rope, cutting rope, retrieving a sea anchor, inflating the floor, bailing, paddling and retrieval of a mannequin into the life raft. During the data collection sessions, participants were asked to repeat these tasks plus two tasks not previously demonstrated (changing flashlight batteries and a patching task) whilst in a 16-person life raft under experimentally simulated ocean conditions.
Results will provide manufacturers, regulators and operators with direction for future life raft design and training in hopes of ensuring higher survival rates for those employing a life raft during evacuation situations.
1. INTRODUCTION
Life rafts have a long history of saving lives at sea since they were introduced onboard ships in 1954 [1].
Following evacuation to a life raft, there are many tasks that are required of the life raft occupants in order to increase the chance of a successful escape and rescue.
Life raft management tasks must be executed quickly and error free to maximize chances for survival.
As a consequence of a life raft’s lightweight design, the system becomes a wobbly structure when deployed in a motion-rich environment. Both physical and cognitive performance has been shown to degrade in a moving environment [2, 3]. Severe motions can interfere with fine and gross motor tasks. Postural interference will increase the time to task completion and likely reduce the quality of the effort.
With motion also comes the potential for motion sickness to occur. Motion sickness can present itself as a mild discomfort or can be so physically debilitating that tasks must be abandoned [4]. As motion sickness symptom severity increases the quality of operator command and control decision-making decreases [5]. Thus it is important that motion effects be considered when delivering life raft survival training and adopting design standards.
Many factors can hinder the ability of an occupant to perform life raft management tasks. While some anecdotal evidence exists regarding how performance may be limited under such conditions, there remains a need to document empirically performance degradations and those factors which impede successful task completion. The purpose of this study was to provide a better understanding of the effects motion have on the ability to perform management tasks considered to be
important for life raft occupant survivability. This information would be invaluable to search and rescue planners, marine evacuation system designers and regulatory bodies governing safety at sea.
2. METHODOLOGY
2.1 SUBJECTS
The Human Investigation Committee of Memorial University of Newfoundland approved the protocol for this study. Twenty-five healthy male subjects (mean age 24.2±4.3years, stature 172.8±5.7cm, mass 78.2±12.0Kg) participated in these experiments. Subjects were informed fully about the procedures and risks of the experiment. Subjects completed a medical history questionnaire and gave written consent prior to the start of the experiment.
Each subject participated in a two-hour training session at the Offshore Safety and Survival Centre (OSSC) of the Marine Institute of Memorial University of Newfoundland. The training session consisted of instruction by survival training experts on life raft management tasks. These tasks included: inflating the life raft floor, securing the canopy, movement within the life raft, painter line cut, painter line tie, sea anchor retrieval, bailing, paddling and retrieving a mannequin from the water into the life raft. Subjects may have had the opportunity to attempt these tasks, although the training did not require the subject to obtain competency.
A simulated puncture patching task and a flashlight battery task were included in the experimental sessions, but not in the training session. These tasks were added to assess how subjects could interpret and execute the
Human Factors in Ship Design, Safety and Operation, London, UK
instructions for these tasks provided within the life raft without the benefit of previous instruction. The scope of this training would be typical for persons seeking employment in offshore settings.
2.2 SIMULATION FACILITIES AND LIFE RAFT All experimental data were collected at the Institute for Ocean Technology (National Research Council), St.
John’s, Newfoundland, CANADA in either the Ocean Engineering Basin (OEB) or the Tow Tank facilities. The OEB uses 168 hydraulically activated wavemakers to generate waves in the 58m (long) x 26m (wide) x 3m (deep) basin. Two simulated ocean conditions were tested in the OEB: 1) calm water condition and 2) mechanically produced irregular waves (significant wave height of 0.58m; peak period of 2.55s) equating to approximately sea state 2 (see Figure 1a). The Tow Tank generates using a dual flap hydraulic wave board and has a total length of 200m with a working area of 120m by 12m and a water depth of 7m (see Figure 1b). The life raft was towed at a speed of 1 m/s (1.94 knots) through both calm water and mechanically generated uni- directional irregular waves (significant wave height of 0.5m and produced a simulated Sea State 2 condition without wind effects) by a single, manned carriage.
(a)
(b)
A new 16 person life raft (DBC Marine Safety Systems, Vancouver BC) was used during these experiments. Both the chambers and canopy of the life raft were inflated and internal pressures were continuously monitored and corrected regularly for consistency. The floor of the life raft was deflated throughout the entirety of the experiment. To ballast the life raft, 8 heavy duty PVC Dacon rescue dummies (Dacon AS, Norway) were filled with water to an approximate weight of 75 kg each and secured to the inside chambers of the life raft. With a combined weight of 8 Dacon mannequins, 2 investigators and 2 subjects, the life raft was ballasted at approximately 75% of its operational capacity.
2.3 DATA ACQUISITION
The OEB and Tow Tank are equipped with a virtual memory system and Windows-based distributed client/server data acquisition system. Data were collected employing standard temporal synchronization of all data streams and were validated by a video recording system.
Two time synchronization markers were used to indicate the start and end of each task. Wave heights were measured with the use of wave probes. Six degree of freedom motions (accelerations: heave, surge and sway and angular rates: roll, pitch and yaw) of the life raft were collected.
Both video monitoring and a handheld stopwatch were used to determine the times to complete tasks. In general, the video records were used to determine the duration of these activities. When there was an obstructed view of the video data of the subjects executing a task, the stopwatch time was employed. The manner and quality of execution in which the subject completed the task was also recorded. All tasks were completed in both the calm and wave conditions.
2.4 PROTOCOL
After demonstrating proficiency in performing the life raft management tasks presented in the training session, participants were asked to repeat them in a 16-person life raft in the two experimental simulated ocean conditions:
calm water/no waves and wave conditions in both the OEB and Tow Tank. The order of condition was randomized, but the OEB and Tow Tank data were collected approximately 4 months apart. Not all tasks were completed in both the OEB and Tow Tank facilities.
Subjects were required to perform these tasks while wearing a SOLAS (safety of life at sea) approved life jacket.
2.5 LIFE RAFT MANAGEMENT TASKS 2.5.1 Canopy closure
Human Factors in Ship Design, Safety and Operation, London, UK
© 2007: The Royal Institution of Naval Architects all three rubber toggles on the outside of the floatation tube, then untie and roll up the inside flap, pulling the drawstring tight and tying it to the tie hanging down from the top of the opening. Both time to completion and quality of closure were recorded.
2.5.2 Painter line cut
The subject began seated with their back to the life raft door. After a start signal was given, the subject was required to remove his knife from the pouch to the left of the door, and cut a rope which was secured to a loop on the bottom of the outside of the life raft to the right of the door (from the exterior). Time to completion was noted when the subject returned to a seated position with the knife and rope in his hands.
2.5.3 Painter line tie
The subject began seated with his back to the life raft door and a rope in his hands. After a start signal was given, the subject was required to lean over the side of the life raft and tie the rope through an exterior loop located on the bottom left of the canopy opening using a two half hitch knot.
2.5.4 Sea anchor retrieval
A sea anchor line was deployed outside the life raft door by an investigator. The subject started seated with his back to the life raft door. After a start signal was given, the subject was required to pull the sea anchor line into the life raft. Time to completion was noted when the subject returned to a seated position with the sea anchor fully inside the life raft.
2.5.5 Bailing
Approximately 1000 litres of water were pumped into the life raft. The subject bailed, for 5 minutes in the OEB trials and for approximately 2 minutes (119.23 r 1.15 sec) in the Tow Tank trials. Bailing was performed using a standard bailer or the equipment bag from which the bailer is stored. Bailing device and motion conditions were randomized.
2.5.6 Mannequin retrieval
A mannequin, weighing 35kg and wearing a SOLAS approved lifejacket, was placed on the boarding ramp outside of the life raft. The subject began the trial seated with his back to the door. The subject was required to bring the mannequin inside the life raft.
2.5.7 Simulated manual inflation of life raft floor A hand pump was used to perform a simulated inflation of the floor of the life raft. The end of the hose of the pump was connected to a flow meter attached to the top air chamber of the interior of the raft which measured the
volume of air pumped and the frequency of pumps. The subject began seated and leaning against the life raft chambers. The subject was required to pump for 10 minutes.
2.5.8 Paddling
The life raft was freed from its towline for this task and the participant was required to lean out of the fore side of the raft and paddle as far as possible in a 5 minute time period using a standard issue plastic life raft paddle. Each subject followed this procedure for two separate trials in both motion conditions. Note that in the wave condition the subject paddled with, rather than against, the waves.
2.5.9 Simulated puncture patching task
The subject was asked to read the instruction sheet from the patch kit issued with the life raft and tell the investigator when they felt confident enough to be able to patch a small leak. The start time commenced when the investigator handed the instruction sheet to the subject.
The subject was then required to answer the question
“after glue is applied to the patch and the damaged area, how long do you have to wait until you apply the patch over the damage?”. The answer to this question was 20 to 30 seconds.
2.5.10 Flashlight battery change task
The subject was handed a waterproof flashlight that was issued with the life raft and a spare set of batteries. The investigator gave the instruction “change the batteries”.
Start time began when the subject was handed the flashlight and stopped when the batteries were successfully changed.
3. RESULTS
Standard parametric procedures were employed to test for significant effects or interactions for wave conditions and repeated measures for each task. While every attempt was made to improve upon the ecological validity of the protocol, it must be acknowledged that these trials were conducted under well controlled conditions and environmental exposures were limited due to the capacities of the test facilities.
While not all task performances demonstrated statistically significant differences between the no motion and wave motion conditions, in all cases there were always trends towards performance decrements due to the addition of waves. Furthermore, in all cases, in which repeated measures were considered in the design, improvements in performance time were noted.
Aggregate data are presented in this section (see Table 1). Full experimental results can be obtained from the authors upon request.
Human Factors in Ship Design, Safety and Operation, London, UK
4. DISCUSSION
The discussion will focus on lessons learned from these experimental trials.
4.1 CANOPY CLOSURE
Leaning out of the raft in high seas conditions creates a risk of a person falling overboard. It would be beneficial to secure the occupant performing this task by providing a harness at the entrance or assigning a co-occupant to hold onto the person performing the task.
Most subjects reported difficulty performing the canopy task. Subjects found it difficult to identify the exterior securing points quickly and often missed them altogether.
A suggestion was made to have large indicator arrows on the outside of the floatation tube pointing to the securing points or to make the colour of these securing points different than the chamber. Another problem was that these securing points protrude externally from the floatation tube and are prone to being damaged during the evacuation process.
The long drawstring often became entangled on the participant (19.1 % of the time) and came undone when the person turned and sat down following closure completion. It is recommended that a more efficient closing system, accessed from inside of the raft be considered in future life raft design.
This discussion considers the importance of the canopy’s ability to keep water out of the life raft. Exposure to cold water could impede fine motor performance in as little as 30 seconds (Cheung, 2003). Further studies could include whether the task could be completed more efficiently while wearing protective gloves.
4.2 PAINTER LINE CUT
The knife is designed to prevent accidental puncturing of the life raft. Subjects noted that it was difficult to identify which was the sharpened, cutting side of the knife. It is recommended that colouring the sharp side or placing an arrow indicating which side is sharp would allow for quick identification and therefore reduce time to complete this task. Clearly identifying the knife storage location within the life raft is important in the time it takes to complete such a task.
4.3 PAINTER LINE TIE
When the subjects attempted to thread the rope though the fabric loop, the loop would tend to stick together when wet. In high waves a person would need one hand to stabilize him or herself while leaning over the life raft.
It was noted that in order to secure the rope more efficiently, the loop on the tow patch should be made of more rigid material than fabric rope. A larger, more rigid loop would have likely enabled them to “thread” the rope more quickly, even with one hand, and reduce the amount of time leaning out of the life raft and decrease the task completion time.
OEB Tow Tank
TASK Calm Waves No Waves Waves
Time (s)
SD (s)
Time (s)
SD (s)
Time (s)
SD (s)
Time (s)
SD (s)
Canopy closure 53.6 10.6 60.4 13 45.4 10.1 48.7 10.2
Painter line cut 13.5 3.9 13.6 4.8 - - - -
Painter line tie 12.3 2.6 13 2.7 - - - -
Sea anchor retrieval 11.1 2.4 11.5 3.3 27.2 6.6 30.4 7.4
Mannequin retrieval 8.5 4.6 8.7 3.9 - - - -
Puncture patching 48.3 8.3 50.6 17.5 - - - -
Flashlight change 51.1 13.3 54.4 23.4 - - - -
Vol. (l)
SD
(l) Vol. (l) SD
(l) Vol. (l) SD (l) Vol.
(l) SD (l) Bailing (bailer) 350.9 130.5 285.4 100.6 132.4 24.1 121.7 29.4 Bailing (equipment bag) 271.6 109.6 238.8 75.9 89.6 34.5 78.6 34.6
Rate (l/s)
SD (l/s)
Rate
(l/s) Rate (l/s)
SD (l/s)
Rate (l/s)
SD (l/s)
Inflation of floor 0.29 0.02 0.28 0.02 - - - -
SD Dist. SD
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© 2007: The Royal Institution of Naval Architects 4.4 SEA ANCHOR RETRIEVAL
For the sea anchor task the subject’s hands were generally exposed to the water. Although testing was carried out in relatively thermo-neutral water, if this had been a cold ocean environment water exposure would limit performance. If exposure of the hands to cold water is likely, as it is in many of the survival tasks, it is recommended that protective gloves which do not impede manual dexterity are made available to life raft occupants.
4.5 BAILING
While both the bailer supplied with the life raft and the equipment bag were available for this task, it became clear that the bailer, while having a smaller volume should be the primary device of choice. The subject who bailed the highest volume of water employed a unique bailing technique. The subject held the bailer in one hand by putting two fingers through the loops on the bailer.
With this technique the subject was able to scoop the water with one hand and push it out of the bailer with the other while in the calm water. In the wave condition, this technique allowed the subject to bail with one hand and use the other hand to stabilize himself against the life raft motions.
4.6 MANNEQUIN RETRIEVAL
The mannequin weight was selected in consideration of participant safety. It is likely that the mass of a survivor retrieved into the life raft would be considerably greater.
It is important that a team strategy be employed in this process, both to protect those doing the retrieving as well as to prevent further injury to the “survivor”. Occupants should be aware of the swell and space inside the life raft should be prepared to situate the survivor following retrieval.
4.7 SIMULATED MANUAL INFLATION OF
LIFE RAFT FLOOR
The task of pumping was found to be an arduous task. It is recommended that frequent rotation of persons assigned to do this task should be considered to improve the time and efficiency in which the floor is inflated.
Occupants not involved in this task should be restricted in movement about the life raft, as movement causes a back pressure from the floor into the pump.
Because the floor inflation task was performed completely within the confines of the canopy, many subjects reported symptoms of motion sickness. Ensuring that the life raft occupants have full view of the horizon (outside view) while performing interior life raft tasks could help to eliminate or minimize the problems of motion sickness. This can be done by opening the canopies whenever weather permits and also by placing pumps in several locations in the life raft to allow the
person pumping to sit in the position least provocative to motion sickness. Perhaps life raft designers should consider installing clear windows in the canopy to allow occupants an opportunity to gaze upon an earth-fixed point of reference. Because of the physical demands of the task, a build up of carbon dioxide, as a bi-product of metabolism, should be expected. In smaller life rafts, a strategy for regular ventilation should be considered.
4.8 PADDLING
In an escape situation occupants should be advised during training to find the direction of the wind and seas if trying to either get clear of a ship or to retrieve a survivor. Depending upon the environmental conditions, paddling in the direction of the waves will likely be the only direction where progress can be achieved and certainly will minimize the amount of energy expenditure by the occupants. Direction of smoke drift and other airborne contaminants should be considered when paddling away from the structure. Occupants should confirm that any painter line securing the life raft has been cut before paddling efforts occur.
If it is expected that the paddling will occur over an extended period of time, a process of substituting paddlers should be considered. Occupants will have to lean out of the life raft to reach the water and it is recommended that another occupant be assigned to hold the paddlers’ feet.
It should be noted that during these experimental trials there was a 7.6% failure rate of the plastic paddles provided with the life raft. Manufacturers should consider constructing paddles from a lightweight, but durable, material to prevent paddles breakage.
4.9 PUNCTURE REPAIR TASK
A puncture repair task must be done quickly and efficiently. Even during daylight, the luminance within the life raft is low. The task instructions should be produced using a large font size as subjects found it difficult to read the instructions in a moving environment.
Subjects also noted the instructions were too ‘wordy’.
Step by step instructions using brief wording, with diagrams would help with task comprehension.
Waterproof instructions would also be useful due to the likely event of water entering the raft or the hands of the occupant being wet.
4.10 FLASHLIGHT BATTERY CHANGE TASK While various flashlight products were not compared, the one provided in this study was not well designed for battery replacement. It is recommended that having an arrow or directions printed directly on the flashlight would significantly reduce the time to effect repairs on the device. Furthermore, the device came with a spare bulb. Similarly, an inexperienced occupant would find it