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Occupational Medicine Advance Access originally published online on May 28, 2008
Occupational Medicine 2008 58(6):400-405; doi:10.1093/occmed/kqn052
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© The Author 2008. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Factors associated with marine injuries during vertical chute evacuation training

Daniel Harwood1 and Alexandra Farrow2

1 Maritime Accident Investigation Board (MAIB), Carlton House, Carlton Place, Southampton SO15 2DZ, UK
2 School of Health Sciences and Social Care, Brunel University, Mary Seacole Building, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

Correspondence to: Alexandra Farrow, School of Health Sciences and Social Care, Brunel University, Mary Seacole Building, Brunel University, Uxbridge, Middlesex UB8 3PH, UK. Tel: +44 1895268759; fax: +44 1895269853; e-mail: alexandra.farrow{at}brunel.ac.uk


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Background The use of a vertical chute marine evacuation system (MES) is now established on marine vessels; this system has, however, been associated with injuries during training.

Aims To identify risk factors associated with adverse outcomes during vertical chute MES training and to generate hypotheses for research into reducing injuries.

Methods Cross-sectional questionnaire study of a cohort of trainees attending vertical chute MES training courses, at two naval training establishments in 2005. Incident data were also collected from both training establishments and from Marine Accident Investigation Branch (MAIB) records.

Results The response rate was 99% (n = 351). Pearson chi square and relative risks (RRs) were calculated for specific outcomes with a number of independent variables. Logistic regression was used to analyse independent variables with a statistically significant (P < 0.05) chi square for the outcome of ‘suffering an injury’ during training. Injury was associated with body mass index denoting ‘overweight’, ‘obese’ or ‘morbidly obese’ with an odds ratio (OR) of 12.7 (95% CI: 2.2-72.7). Participants below the mean height also had increased risk of suffering an injury during training (OR: 4.8; 95% CI: 1.2-18.5). Phobias and apprehension prior to training increased the risk of injury; reporting of ‘some concern over the dark’ was statistically significant (OR: 16.6; 95% CI: 1.6-171.5). Life jacket discomfort was also significantly associated with suffering an injury.

Conclusion Policy implications include alteration of the MES design and management of risk through training and informed decision making for choosing an evacuation system for ships and ferries.

Keywords      Occupation; risk; seafarers


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Although traditional lifeboats are intended to save life, many seafarers have been seriously injured or killed during the routine launching and recovery of these essential ‘life saving appliances’ (LSAs) [1–5], decreasing confidence in their effectiveness [6,7] and increasing pressure on the industry to develop and introduce new methods of safely evacuating ships [7–9]. LSAs have evolved considerably in recent years with greater emphasis on the rapid, dry-shod evacuation of large numbers of people into inflatable life rafts.

Many varieties of marine evacuation systems (MESs) are in use worldwide, with earlier designs using slides similar to those on aircraft. The MES investigated during this study is claimed, by the manufacturer [9], to be the first truly dry-shod system allowing evacuees-free descent, under the arresting control of friction, through a telescopic vertical chute directly into a fully enclosed life raft. The chutes, ranging between 8 and 20 m in height, comprise 1-m long interlinked cells, each containing an elasticized descent-arresting sock and are designed to evacuate up to 430 people in <20 min (Figure 1). A number of incidents, including one fatality [10,11] have occurred while using this award winning MES [9] during ship evacuation training.


Figure 1
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  		Figure 1. Vertical chute MES.

 
Over the last century, maritime legislation has evolved in the aftermath of disasters such as the Titanic, the Herald of Free Enterprise and the Estonia [12]. The Marine Accident Investigation Branch (MAIB) [10] stated that to the best of their knowledge a vertical chute MES had not yet been used in a real emergency. Therefore, studies such as this should help to identify hazards and quantify risks associated with these LSAs and possibly help influence improvements without having to wait for the impetus of hindsight.

The literature search highlighted a general scarcity of published peer reviewed research on this subject. It has been suggested that the pressures of commercial competition and the potential impact of negative publicity has resulted in a reluctance by shipping companies to publish emergency ship evacuation research and data [13–15], providing an impetus for undertaking this study.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conflicts of interest
 References
 
This cross-sectional study involved analysis of data from anonymous self-administered questionnaires presented to trainees attending sea survival courses, involving the use of a vertical chute MES, at two training establishments between April and May 2005. Establishment ‘A’ was a military training school operated by the Royal Navy (RN) while establishment ‘B’ was a commercial training centre operated by a leading UK passenger ferry company. Questionnaires were completed voluntarily during the training course.

Questions ascertained physiological and sociodemographic characteristics, physical experiences during training serials, participants’ phobias, preferences for different evacuation methods and four questions relating to injuries during training. The four adverse outcomes considered were as follows:

(i) Stopping or getting stuck in the chute.
(ii) Leg impaction with the sides of the raft.
(iii) Exiting the chute in an undesirable position.
(iv) Discomfort caused by the life jacket worn.

The Statistical Package for the Social Sciences (SPSS) (version 11.5) was used to analyse the data, resulting in the generation of 49 dichotomous variables after recoding. Pearson chi-square values and relative risks (RRs) were calculated with cross-tabulations. The Fishers exact chi-square value was quoted for expected counts of less than five. Initial analysis identified any statistically significant associations between injuries suffered and the four adverse outcomes above. Further analysis identified any statistically significant associations between these adverse outcomes and factors acting as independent variables. Logistic regression (LR) analysis was applied to determine the odds ratio (OR) for ‘suffer any injury’ during training and dichotomous independent variables identified from cross-tabulation analysis. Those independent variables associated with an outcome with a Pearson chi-square P value of ≤0.05 were included in the LR models.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conflicts of interest
 References
 
A total of 351 completed questionnaires were analysed, a response rate of 99% from establishments A (n = 244) and B (n = 107). The participants were employed by a variety of organizations, with 46% from the RN (n = 160) and 30% the Merchant Navy (MN) (n = 107). There were 26% (n = 90) employed for <2 years, 54% (n = 185) for 2–10 years and 20% (n = 68) for >10 years; 81% were male. Ratios of male to female participants differed between the two establishments; B had 32% female participants compared to A with 14%. This reflects an employee population in A of 40 191 RN personnel, 91% male, and establishment B of 3342 sea staff, 78% male (employee levels for August 2005). Participant ages were categorized into <21, 21–40 and >40 years of age.

Participants from the MN attending courses at establishment B were older, 39% over age 40 years compared with 5% at A. There were 22% of participants at A <21 years compared to 7% at B. These statistics represent the expected age profiles within the populations of these organizations, the younger military profile reflecting a relatively short career of 21 years, and the older age profile of the MN personnel reflecting an increasingly ageing population. The mean heights were 1.79 m for males and 1.65 m for females. Mean body mass index (BMI) was 24.8 kg/m2 for males and 23.7 kg/m2 for females. The World Health Organization (WHO) categories for BMI are <18.5 kg/m2 = ‘underweight’; 18.5–25 kg/m2 = ‘healthy’; 25.0–30 kg/m2 = ‘overweight’; 30.0–40 kg/m2 = ‘obese’ and >40.0 kg/m2 = ‘morbidly obese’.

Previous training on this type of MES was reported by 32% (n = 113) of participants. The MN ferry employees from B were more experienced in MES training, with 88% (n = 94) reporting previous descents, compared to 8% (n = 19) of trainees from A. Temporarily stopping in the chute during descent was reported by 8% (n = 27) while 8% (n = 29) reported attempting to control their speed. Of the respondents, 87% (n = 284) reported exiting the chute in the desired manner (i.e. facing forwards into the raft), 4% (n = 14) reported exiting backwards (facing into the chute), 9% (n = 28) reported exiting sideways and 1% (n = 2) stated ‘other’. These results were recoded into ‘desired exit position’ and ‘undesirable exit position’; 13% (n = 44) exiting the chute in an undesirable position. Of 97% (n = 340) responding to the question relating to life jackets, 8% (n = 27) reported their life jacket caused discomfort while descending the chute but gender differences were not statistically significant. Legs impacting on the side of the raft were reported by 20% (n = 65), with 6% (n = 4) rating the impact as ‘heavy’. Self-assessed speed of descent was anticipated by 60% (n = 205), while 21% (n = 70) felt their descent was faster and 19% (n = 65) slower than anticipated.

The psychological aspects of the respondents’ training experience were rated by 94% (n = 322) as ‘average’ to ‘exhilarating’ while 6% (n = 19) rated the experience as ‘uncomfortable’ to ‘disturbing’. Suffering some degree of concern relating to four phobias was reported by 41% (n = 144). However, only 18% (n = 62) felt some level of concern during training with respect to phobias. Of participants answering preference of method for ship evacuation, 56% (n = 99) reported that the vertical chute MES offered the best chance of survival for themselves in a real incident and 70% (n = 123) that MESs in general offered them the best means of escape. Interestingly, a much larger percentage (79%) reported the vertical chute MES as the best method of evacuation to save as many people as possible and 93% (n = 154) that MESs generally offered the best means of escape for all onboard. By contrast, only 5% of respondents considered the traditional davit launched lifeboat to offer the best chance of self-preservation in an emergency and 1% thought they offered the best method of saving the majority. Injuries during training descents were stated by 4% (n = 15) of respondents, none were classified as major or serious [15,16]. One per cent stated they had reported the injury while 3% (n = 12) said they had not. In addition, 2% reported previously suffering injuries during sea survival training. Types of injuries were classed as ‘impact’ injuries such as sprains, strains, aches, bruises and friction burns. Respondents in the BMI categories of overweight to morbidly obese had a statistically significant (P < 0.001) increased RR of 2.3 (95% CI: 1.8–2.9) of suffering an injury during training. There was a statistically significant (P < 0.01) association between height and suffering an injury, with those below the mean height having an increased RR of 1.9 (95% CI: 1.4–2.5). Suffering an injury during training was also associated with life jacket discomfort (RR: 4.2; 95% CI: 1.7–10.7) and with reporting some level of fear relating to any of the phobias in the questionnaire (RR: 1.6; 95% CI: 1.1–2.3). Feeling concern over heights and the dark was statistically significantly associated with suffering an injury, but the wide confidence intervals reflected the small numbers affected. There was a statistically significant association (P < 0.05) between suffering any injury and rating the training experience as uncomfortable to disturbing.

A temporary stop in the chute was associated with reporting life jacket discomfort with an increased RR of 2.9 (95% CI: 1.2–6.9) (P < 0.05). Participants from establishment B had an increased RR of 1.7 (95% CI: 1.1–2.6) of stopping temporarily in the chute compared to those from A.

Reporting of leg impacts on the raft sides was not statistically significantly associated with suffering an injury. However, respondents experiencing life jacket discomfort had an increased RR of 2.4 (95% CI: 1.1, 4.9) of suffering leg impact (P < 0.05). Those rating their speed of descent as ‘not as expected’ had an increased RR of 1.5 (95% CI: 1.1, 1.9) of experiencing an impact (P < 0.05). Reporting feeling nervous prior to training or needing encouragement to drop into the chute had RRs of 1.94 (95% CI: 1.2, 3.1) and 5.8 (95% CI: 2.3, 14.7), respectively, for reporting an impact with the side of the raft.

With respect to exit orientation, questionnaire data did not identify any statistically significant associations but participants who stated that they had stopped momentarily in the chute, attempted to control their speed of descent, felt nervous prior to the training serial or suffered from phobias were shown to have an increased risk of exiting in an undesirable position. Suffering from claustrophobia, feeling claustrophobic, feeling concern over the dark and rating the training experience as uncomfortable to disturbing were statistically significantly associated with experiencing life jacket discomfort (Table 1).


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  		Table 1. Statistically significant associations identified during cross-tabulation

 
Female participants were almost twice as likely (65% compared to 36%) to report some level of fear compared to males [17]. A greater percentage of participants trained at B (58%, n = 61) reported suffering some level of phobia compared to those at A (34%, n = 83). A similar percentage of males at both establishments reported the training caused concern relating to these phobias; 53% of females from establishment B declared concern compared to 24% from A. A statistically significant (P < 0.001) increased percentage of respondents from B (13%, n = 13) rated the training experience as uncomfortable to disturbing compared to those from establishment A (3%, n = 6) (Table 2).


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  		Table 2. LR models

 
The first LR model for ‘suffer any injury’ included the physiological independent variables of BMI (dichotomized using WHO standards [18]) and height (dichotomized about the mean). Suffer any injury was statistically significantly associated with BMI and height. Overweight to morbidly obese trainees had an increased OR of 9.6 (95% CI: 2.1, 43.9) of suffering an injury during training. Participants below the mean height also had a statistically significant (P < 0.05) increased odds of suffering an injury during training OR of 4.7 (95% CI: 1.3, 17.6).

The second LR for suffer any injury addressed the psychological aspects of the training evolution with ‘suffer some level of phobia’, ‘felt some concern over the dark’ and ‘felt some concern over height’ included in the model. Those participants feeling some concern over the dark had a statistically significant (P < 0.05) increased odds of suffering injury during training with an OR of 6.3 (95% CI: 1.0, 39.2).

The final LR model for suffer any injury considered the statistically significant independent variables from the first two models (BMI, height and felt some concern over the dark) as well as ‘life jacket discomfort’. BMI was associated with suffering an injury (P < 0.01), as were height and felt some concern over the dark (P < 0.05); life jacket discomfort was not statistically significant.

When analysed together, BMI, height and felt some concern over the dark, all remained significantly related to suffering injury during training. The strongest relationships were felt some concern over the dark and BMI with OR of 16.6 (95% CI: 1.6, 171.5) and 12.7 (95% CI: 2.2, 72.7), respectively. Multifactorial analysis did not reduce the ORs, suggesting these factors were acting independently of each other.


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conflicts of interest
 References
 
The principal study findings were that suffering an injury during training was associated with an overweight, obese or morbidly obese BMI (OR: 12.7; 95% CI: 2.2, 72.7) and with height below the mean (OR: 4.8; 95% CI: 1.2, 18.5). Phobias and apprehension prior to training and life jacket discomfort were also significantly associated with suffering an injury.

The strengths of the study include the sample population, a defined cohort of trainees free from selection bias and representative of the total employee populations undergoing training at both establishments. Time to complete questionnaires during training was prearranged, facilitating a high-response rate (99%, n = 351) and reducing recall bias, although the effects of minor sprains, strains and bruising may not have been fully evident prior to questionnaire completion. To eliminate commercial bias, equipment manufacturers, who have exploited maritime journals to promote their products [9] and discredit those of competitors [19,20], were not consulted during this study.

Questionnaires from establishment B had more missing data, possibly because of some military jargon in the questionnaire or because a number of questionnaires from B had been printed on both sides, suggesting that subjects might have missed some pages.

Individuals getting stuck in the chute can experience catastrophic outcomes [21]. This in turn can seriously affect the efficiency of the system, increasing the risk of multiple fatalities due to increased time taken to abandon ship. Eight per cent of respondents reported temporarily stopping in the chutes; analysis highlighted the impact that having a phobia or being nervous prior to training had on the outcome of suffering an injury. The present study supports the hypothesis of Denison et al. [21] that suffering from claustrophobia may negatively impact on evacuees descending these chutes. While female participants were almost twice as likely to suffer a phobia as males, Fredrikson et al. suggest that social transmission of fears may be more frequent among women than men [17]. Concern over the dark and fear of heights, however, were found to be more significant when the outcome was suffering an injury. It is important to emphasize that the study participants were relatively fit seafarers or military personnel undergoing training in a well-illuminated controlled environment, on dry land, using realistic MES rigs.

Life jackets have previously been found to be associated with reported injuries [10,11,21] and this is supported by the present study. The traditional MN ‘Board of Trade’ life jackets used onboard passenger ships are designed to meet the International Maritime Organization's regulations. These bulky life jackets, manufactured using rigid buoyancy materials, increase the evacuee's upper torso diameter and tend to lift up, causing discomfort or injury to personnel descending the chutes. Despite design changes, participants experiencing discomfort attributed to life jackets were at an increased risk of suffering an injury, stopping in the chute or suffering an impact on entry into the life raft. Interestingly, both establishments reported similar levels of discomfort despite one using the rigid MN Board of Trade life jacket (with leg straps) and the other using the inflatable RN ‘general service’ life jacket (without leg straps).

A number of injuries have occurred during training and deployment exercises as a result of trainee's legs impacting on the rigid buoyancy tubes of the sides of the life rafts. This was exacerbated by the fact that one of the MES's two chutes was oriented such that the exit cell faced towards the side of the raft. This was of such concern to one ferry company [10] that their risk assessment did not allow the affected chutes to be used during system deployments. This problem was also apparent on the training rigs; however, both training establishments repositioned their chutes to face the centre of the raft prior to the commencement of this study.

The lack of previously published research in this area has made it difficult for direct comparisons between the present study and other projects. The MAIB's [10] incident investigation report was supported by research from independent specialists, the equipment manufacturer, the MCA and P&O Ferries Ltd. The latter (P&O Ferries, 2003) had used a postal questionnaire to collate data on employees’ experiences during shipboard vertical chute MES deployments. The 79 questionnaires returned (response rate unknown) were completed on a voluntary basis but were not anonymous. The company's questionnaire focussed on the impact of life jackets but nevertheless some comparisons could be made with this study. Of respondents to the ferry company's postal questionnaire, 18% (n = 14) reported suffering injuries during the evacuation exercises compared to 5% (n = 15) reported in this study. Stopping temporarily in the chute was reported by 23% (n = 18) of the company's respondents compared to 8% (n = 27) of respondents in the present study, suggesting that the longer chutes fitted to ships may give rise to an increased incidence of suffering an injury or stopping in the chute compared to the training rigs. The ferry company's data were collected prior to improvements in life jacket design.

The present study confirms that professional seafarers consider that MESs offer the best means of escape for all onboard ship in an emergency evacuation. However, a number of physical and psychological characteristics affect the risk of injury in using such systems and some traditional life jacket designs also appear to impair the efficiency of MESs and increase the risk of injury to users, suggesting the need for life jacket design improvements.


Key points
  • Individual physique, psychological characteristics and life jackets impact on the effectiveness of the system; short and heavy trainees are the most vulnerable with increased odds of suffering an injury.
  • Seventy-nine per cent of respondents reported vertical chute MES offered the best chance of saving as many people as possible in an emergency.
  • Appropriate training and well-briefed operators should reduce adverse outcomes.

 


   Conflicts of interest
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
References
 
None declared.


   Acknowledgements
 
We would like to thank all respondents for completing the questionnaires.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 

  1. MAIB. Review of Lifeboat and Launching Systems’ Accidents. Safety Study. London: MAIB, 2001. http://www.maib.gov.uk/cms_resources/Review_of_%20lifeboat_and_launching_systems_accidents.pdf.

  2. MAIB. Report of the Investigation of the Lifeboat Release Gear Test on RFA Fort Victoria Which Caused Injuries to Two People at Falmouth Ship Repair Yard. Marine Accident Report. London: MAIB, 2005. http://www.maib.gov.uk/cms_resources/Review_of_%20lifeboat_and_launching_systems_accidents.pdf.

  3. Australian Transport Safety Bureau (ATSB). Lifeboat accidents. Saf Bull (2003) www.atsb.gov.au/publications.

  4. IMO. Casualty Statistics and Investigations; Accidents Involving Lifesaving Appliances. In: IMO sub-committee on flag state implementation (2004) 12th session, Agenda item 4. HMSO. http://www.imo.org/includes/blastDataOnly.asp/data_id%3D10107/IMONews_204corrected.pdf.

  5. Lifeboat Safety; Safety of Seafarers. MER 2002; Oct:24–25.

  6. OCIMF, Intertanko, Sigtto. Lifeboat Incident Survey. Joint Industry Survey. Oil Companies International Forum, 2000, London. http://www.ocimf.com/view_document.cfm?id=340.

  7. Anon. Time for a life saving re-think. Naval Architect (2003) 3.

  8. Barber D. Float-free accommodation modules—a radical solution to bulker safety. Naval Architect (2003) 54–56.

  9. Cruise & Ferry Info. Maritime Survival Systems; Ideas and Innovations. Vol. 6–7. London, 1999.

  10. MAIB. Report on the Investigation of a Fatal Accident During a Vertical Chute Evacuation Drill from the UK Registered Ro-Ro Ferry P&OSL Aquitaine in Dover harbour on 9th October (2003) 2002. Marine Accident Report. London: MAIB. http://www.maib.gov.uk/cms_resources/aquitaine-chute.pdf.

  11. MCA. Operational issues relating to Marine Evacuation Systems (2004) Marine Guidance Note. 273 (M). http://www.mcga.gov.uk/c4mca/mcga07-home/newsandpublications.htm.

  12. Harwood S. (1998) A Review of Marine Accidents Which Have Led to Changes in Regulations. London: The Nautical Institute, 1998. http://www.nautinst.org/search/mis/.

  13. Sharp G, Gwynne S, Galea ER. The Effects of Ship Motion on the Evacuation Process, Subsection 3.3, Collection and Analysis of Available Data from Controlled Experiments/Drills or Actual Evacuations. Maritime and Coastguard Agency Research Project 490. London: University of Greenwich, 2003.

  14. Vassalos C, Vassalos D. The Effects of Ship Motion on the Evacuation Process: Summary Report. Research Project 490, Phase 1. Ships Stability Research Centre, Universities of Glasgow and Strathclyde, 2004. http://www.mcga.gov.uk/c4mca/lrgtxt/rp490_task_3.1a_+_appendix.pdf.

  15. MCA. (2005) Accident Reporting and Investigation. Marine Guidance Note. 289 (M+F), 2005. http://www.mcga.gov.uk/c4mca/mcga07-home/newsandpublications.htm.

  16. Department for Transport 13496 No. 881. The Merchant Shipping (Accident Reporting and Investigation) Regulations. London: MAIB, 2005. http://www.maib.dft.gov.uk/cms_resources/Regulations%202005.pdf.

  17. Fredrikson M, Annas P, Fischer H, Wik G. Gender and age differences in the prevalence of specific fears and phobias. Behav Res Ther (1996) 34:33–39.[CrossRef][Web of Science][Medline]

  18. WHO. Obesity: Preventing and Managing the Global Epidemic (1998) Report of the World Health Organisation Consultation on Obesity.

  19. Grainger M. Evacuation systems come under scrutiny. Saf Sea Int (2005) 39:24–25.

  20. Grainger M. Ferry vertical-chute evacuation systems ‘may not be safe’. Lloyds List, 58358:16, 2003.

  21. Denison DM, Mills M, Mort A, Hilditch R, Porter A. An Investigation into the Role of Positional Asphyxia in the Death of a Volunteer Taking Part in a Trial of a Maritime Mass-Evacuation System. Report No. 18/2003. QinetiQ,KI/CHS/CR031611/1.0. London: MAIB, 2003. http://www.maib.gov.uk/cms_resources/aquitaine-chute.pdf.


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