Habitability in Berthing Compartments and Well-Being of Sailors Working on U.S. Navy Surface Ships

Abstract

Objective

The study had two objectives: (a) to assess the prevalence of sleep-related habitability concerns in the berthing compartments of U.S. Navy surface ships and (b) to assess whether habitability issues in berthing compartments affected the sleep and well-being of crew members.

Background

The importance of habitability for human well-being is recognized. Little is known, however, about the association between habitability factors in the sleeping/berthing compartments and sailor well-being in operational conditions.

Method

Fit-for-duty sailors (N = 1,269; from six ships) participated in this naturalistic and longitudinal study. Sailors reported habitability factors affecting their sleep and completed four standardized questionnaires to assess daytime sleepiness, insomnia, sleep quality, and mood. Sleep was assessed through wrist-worn actigraphy and activity logs.

Results

Noise, ambient temperature, poor bedding conditions, and ambient light were the most frequently reported factors of concern. Compared to their peers with fewer complaints, sailors with more habitability-related complaints were more likely to have elevated daytime sleepiness (by 23%) and to report insomnia symptoms (145%) and lower sleep quality (21%). Sailors who reported more habitability-related issues also tended to sleep longer. Individuals with more complaints about habitability also tended to report worse mood (total mood disturbance, tension/anxiety, depression, fatigue, and confusion/bewilderment).

Conclusion

Habitability-related complaints are associated with sailor well-being and sleep. Future studies should expound on the various detrimental factors that degrade conditions in berthing compartments and negatively impact crew well-being.

Application

Habitability in berthing compartments of surface ships is associated with sailors’ daytime sleepiness, insomnia severity, mood, and sleep attributes. Ship designers should take these findings into consideration and investigate viable and cost-effective methods to mitigate the problems we identified.

Keywords

naval ships habitability sleep insomnia mood sleep disruptions noise temperature light

Introduction

Even though there are multiple definitions of habitability, the term generally refers to how suitable an environment is for human occupation and use (Lantrip, 1997). On naval vessels, habitability describes all the factors which collectively make up the environment in which the ship’s company is required to live and work efficiently (NATO, 1991). Along these lines, the American Society for Testing and Materials (ASTM) assumes that ship characteristics, the facilities available on the ship, access to personal services, and living and working conditions are all integral parts of habitability (ASTM, 2015).

The current policy and the details of the shipboard habitability program of the Chief of the Naval Operations (OPNAV) are provided in Instruction 9640.1C (OPNAV, 2019). The provisions of OPNAVINST 9640.1 are implemented in manual T9640-AC-DSP-010/HAB (NAVSEA, 2016). Overall, the purpose of the NAVSEA document is to establish U.S. Navy shipboard habitability design criteria and practices, which will ensure unit mission readiness and provide an acceptable level of quality of life for sailors, marines, and other detachments (NAVSEA, 2016). The provisions of T9640-AC-DSP-010/HAB address a wide range of habitability aspects of manned spaces, that is, any ship compartment occupied by crew members continuously for more than 20 min. For example, it addresses environmental factors such as temperature, humidity, air flow/velocity, atmospheric contaminants, noise (addressed in MIL-STD-1474), lighting, whole-body vibration (addressed in ISO 6954 and MIL-STD-1472), dimensional characteristics of spaces and furniture, food service, hygiene and sanitation, relaxation, religious activity and personal study, recreation, offices and work spaces, and communal services (DoD, 2012; DoD, 2015; ISO, 2000; NAVSEA, 2016).

Research has provided evidence that habitability is associated with aspects of sailor well-being. The U.S. Navy Atlantic Fleet Inspector General (1969) survey of 71 surface ships identified that one of the most serious deficiencies reported by sailors was difficulty in sleeping due to noise, overcrowding, and inadequate bunks, whereas Broedling (1970) reported that poor living conditions decreased sailor desire to stay in the Navy (as cited in Wilcove & Schwerin, 2008, p. 117). Later data from the 2002 Navy Quality of Life survey showed that enlisted sailors were dissatisfied with personnel storage space (69%), room in the berthing compartment (66%), rack space (65%), privacy (63%), mattresses (54%), and the berthing area (52%; Wilcove, 2006). Wilcove et al. (2003) used data from the Navy Quality of Life survey to show that satisfaction with shipboard life (to include habitability factors) was associated with personnel intention to reenlist, career continuance plans, and job performance (Wilcove et al., 2009). In 2008, Wilcove and Schwerin (2008) showed that conditions in the berthing compartments and privacy were negatively associated with crew retention.

Of specific interest to our study, however, is habitability in the areas in which the crew sleeps. Our focus on berthing compartments, as they are called in the Navy, stems from our studies over the last 15 years. Data collections from more than 30 ships have clearly shown that sleep deprivation, endemic in the naval operational environment, affects crew well-being, mood, and performance (Miller et al., 2012; Shattuck et al., 2019). Sailors are chronically deprived of “normal” sleep along any of three dimensions, that is, duration, timing, and quality of sleep (Shattuck & Matsangas, 2015a, 2015b; Matsangas & Shattuck, 2016). Therefore, a question arises about whether habitability issues in the berthing compartments are associated with sailor alertness and well-being. We recently presented findings from a sample of United States Navy (USN) sailors regarding the prevalence of habitability concerns (Matsangas & Shattuck, 2017). Sailors reported that environmental conditions (e.g., temperature, noise, light, air quality/odors, ventilation, ship motion) in berthing spaces affect the quality of their sleep. Of note, a study on 21 ships of the Royal Norwegian Navy showed that exposure to noise during sleep was associated with increased movements during sleep, resulting in reduced sleep efficiency (Sunde et al., 2016).

Our review of the research literature identified two points of interest. First, few studies have focused explicitly on the conditions in berthing compartments of naval ships and how these conditions affect crew sleep. Second, the studies we reviewed were based, in general, on self-reported data obtained using surveys. With these concerns in mind, our study had two goals. First, we assessed the prevalence of sleep-related habitability concerns in the berthing compartments of U.S. Navy surface ships. Second, we assessed whether habitability issues in berthing compartments affected the sleep and well-being of crew members. We hypothesized that sailor well-being would be associated with habitability-related complaints. Compared to their peers with fewer complaints, sailors with more complaints would have more severe daytime sleepiness and insomnia symptoms, worse sleep patterns, and worse mood.

Method

Participants

Sailors from five ships of the U.S. Navy (one Nimitz-class aircraft carrier, one Ticonderoga-class cruisers, three Arleigh Burke-class Flight IIA destroyers) participated in the study. All participants were deemed to be “fit for duty” and were observed while performing their normal shipboard activities. This research complied with the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board at the Naval Postgraduate School. Informed consent was obtained from each participant.

Apparatus and Measurements

The 19-item Pittsburgh Sleep Quality Index (PSQI) was used to assess sleep quality (Buysse et al., 1989). The PSQI total score ranged from 0 (better) to 21 (worse). Individuals with a PSQI total score ≤ 5 are characterized as good sleepers, whereas scores > 5 are associated with poor sleep quality. The Epworth Sleepiness Scale (ESS) was used to assess average daytime sleepiness (Johns, 1991). Responses to the eight items on the tool were summed together for the total score. A sum of more than 10 indicates elevated daytime sleepiness (Johns, 1992). The 7-item Insomnia Severity Index (ISI) was used to assess the severity of both nighttime and daytime components of insomnia (Bastien et al., 2001; Morin et al., 2011). The ISI score results from the sum of all seven items. A score of 15 or more on the ISI is associated with moderate to severe insomnia.

To measure mood states, participants completed the 65-item Profile of Mood States (POMS; McNair et al., 1971). The POMS questionnaire assesses multiple dimensions of the mood construct using six subscales: anger–hostility (12 items; range 0–48), confusion–bewilderment (7 items; range 0–28), depression (15 items; range 0–60), fatigue (7 items; range 0–28), tension–anxiety (9 items; range 0–36), and vigor–activity (8 items; range 0–32). A Total Mood Disturbance (TMD) score is derived by adding the five subscales (range 0–200) and subtracting the vigor score from the total score. The prestudy questionnaire included items regarding demographics (age, gender, rate/rank, and department) and habitability-related factors in the berthing compartments that could potentially affect sailor sleep. At the end of the underway data collection period, participants completed the poststudy questionnaire in which they completed the ESS, ISI, PSQI, and POMS scales and reported whether they had been standing watch during the underway.

Sleep was assessed unobtrusively with actigraphy, a validated method to assess sleep and wake patterns in field settings for long periods of time (Ancoli-Israel et al., 2015; Morgenthaler et al., 2007). We used two wrist-worn devices which collected only activity data: the Motionlogger Watch (Ambulatory Monitoring, Inc. [AMI]; Ardsley, NY) and the Spectrum Plus (Philips-Respironics [PR]; Bend, OR). AMI data (collected in the Zero-Crossing Mode) were scored using Action W version 2.7.2155 software with the Cole–Kripke algorithm for rescoring. The criterion for sleep and wake episodes was 5 min. The sleep latency criterion was no more than 1 min awake in a 20-min period (all values are default for this software). PR data were scored using Actiware software version 6.0.0 (Philips Respironics). The medium sensitivity threshold (40 counts per epoch) was used, with 10 immobile minutes as the criterion for sleep onset and sleep end (all values are default for this software). Data for both devices were collected in 1-min epochs. Previous research has shown that AMI data analyzed with Cole–Kripke and PR data analyzed with medium sensitivity parameters assess total sleep time for an approximately 8-hr night sleep episode with 3-min precision (Meltzer et al., 2012).

A known limitation of actigraphy is misclassifying periods of inactivity as sleep. To overcome this issue, we used information from the activity logs to manually determine start and end times of rest intervals using the actigraphy data as the primary source for the sleep analysis. Within each rest interval, the actigraphically assessed sleep was automatically calculated. Next, data were retrieved to develop the database of sleep intervals. The AMI device uses the Infrared Data Association wireless optical communication protocol to transmit data, whereas the PR device uses the Universal Serial Bus protocol.

Procedures

The data presented herein are a subset of measures from multiple field assessments of crew members on six USN ships between 2014 and 2017. Two methods were utilized to obtain the data. Data were collected using a prospective naturalistic design with an underway data collection period of 7–18 days. Sailors completed the study questionnaires at the beginning and end of the study. During the data collection period, sailors were asked to wear an actiwatch and complete an activity log. If sailors could not participate in the longitudinal protocol due to operational/work constraints, they were given a one-time only opportunity to complete the combined questionnaire once (that included demographic and habitability questions, ESS, ISI, and PSQI). At the beginning of all data collections, sailors had been on the same daily schedule for at least 3 days.

Analytical Plan

Initially, 919 sailors were enrolled (Figure 1). Those sailors with missing habitability data (n = 27) were excluded. Therefore, analysis was based on 892 sailors, 652 sailors with POMS data and 573 sailors with actigraphy data. Sailors were classified into five groups based on their work schedule. Watchstanders included those sailors who stood watch on either a rotating or fixed watchstanding schedule. A watch is the period of time during which a sailor is assigned a specific, detailed responsibility on a recurring basis (Department of the Navy, 2012). The two major rotating schedules that were used were the 5-hr on/10-hr off (i.e., standing watch for 5 hr followed by 10-hr off watch, leading to a pattern repeating every 3 days) and the 5-hr on/15-hr off (standing watch for 5 hr followed by 15-hr off watch, leading to a pattern repeating every 4 days). The nonwatchstanders were divided into three subgroups. The “maintenance shiftworkers” included sailors working 12-hr shifts performing maintenance. The “galley workers” included sailors involved in food preparation who worked long hours in the galley. Lastly, “dayworkers” included sailors who worked normal daytime hours, often with a significantly lighter work schedule.

Figure 1

Habitability-related factors affecting sailor sleep (horizontal lines denote the standard error of the mean). PA = public announcement.

Sleep analysis was based on two variables, daily sleep duration (calculated as the sum of all sleep within a 24-hr period from midnight to midnight) and number of sleep episodes per day (the number of rest episodes within a 24-hr period from midnight to midnight). Both sleep variables were aggregated by participant.

First, all data were screened for erroneous/anomalous entries and underwent descriptive statistical analysis. Next, we assessed the prevalence of habitability-related issues. Multiple regression analysis was used to assess whether habitability issues were associated with sailors’ well-being in terms of daytime sleepiness (ESS score), insomnia symptoms (ISI score), sleep quality (PSQI global score), mood (POMS scores), and sleep attributes (daily sleep duration, number of sleep episodes/day). Analysis was based on two groups of models. The first group included the number of habitability-related issues reported by each sailor (ranging from 0 to 13) as the potential predictor factor. The second group of models included noise, temperature, light in the berthing compartment, ship motion, bedding conditions (to include mattress, bed size, pillow, and rack curtain), and odors as potential predictor variables. Ship, gender, rank group, and occupational group were used as confounding factors in all models. Lastly, we classified sailors into quartile groups based on the number of reported habitability issues. Two quartile groups were compared using the distribution of the number of reported issues. The lower quartile (or fewer issues group) was defined as personnel who were in the 25th percentile or lower; and the high quartile (or higher issues group) was defined as personnel who fell in the 75th percentile or greater. Statistical comparisons were made between the lower and upper quartiles.

Statistical analysis was conducted with JMP statistical software (JMP Pro 14; SAS Institute; Cary, NC). Data normality was assessed with the Shapiro–Wilk W test. Data were compared using the Wilcoxon Rank Sum test and Fisher’s exact test. An alpha level of .05 was used to determine statistical significance. Post hoc statistical significance was assessed using the Benjamini–Hochberg False Discovery Rate (BH-FDR) controlling procedure (Benjamini & Hochberg, 1995) with q = 0.20. Effect size metrics were calculated for statistically significant differences, effect size r for continuous variables, and relative risk with 95% confidence intervals for categorical variables. Summary data are reported as mean ± standard deviation or median (interquartile range [IQR]) as appropriate. Imputation was not applied to missing POMS and actigraphy data. Missing data did not show a systematic pattern.

Results

Participants had a median age of 25 years (IQR = 8), were predominantly males (703, 78.7%), and were enlisted personnel (777, 87.1%). Most sailors were on destroyers (346, 38.8%), followed by sailors on cruisers (289, 32.4%) and sailors on the aircraft carrier (257, 28.8%). Detailed demographics are shown in Table 1.

Table 1

Demographic Information of the Study Sample

Age in years, MD ± IQR	25 ± 8
Sex (males), # (%)	703 (78.8)
Enlisted personnel, # (%)	777 (87.1)
E1–E3	108 (12.1)
E4–E6	614 (68.8)
E7–E9	55 (6.17)
Officers, # (%)	115 (12.9)
O1–O3	100 (11.2)
O4–O6	15 (1.67)
Department, # (%)
Air	17 (1.91)
Combat Systems	111 (12.4)
Engineering	110 (12.3)
Executive/Admin	67 (7.51)
Medical	8 (0.90)
Operations	131 (14.7)
Plans and Tactics	48 (5.38)
Reactor	238 (26.7)
Supply	90 (10.1)
Weapons	70 (7.85)
Years on active duty, MD ± IQR	4 ± 5.5

Note. IQR = interquartile range; MD = median.

As assessed by actigraphy, participants slept on average 6.66 ± .958 hr daily (ranging from 3.30 to 9.12 hr) split into an average of 1.38 episodes per day (IQR = 0.607, range = 0.778–2.90). The average ESS score was 10.0 ± 4.41 (ranging from 0 to 24) with 45.1% of the participants having elevated daytime sleepiness (ESS > 10). The average ISI score was 10.9 ± 4.92 (ranging from 0 to 26) with 21.6% of the participants reporting ISI symptoms which classified them in the clinical insomnia (moderate severity and severe) groups (ISI ≥ 15). The average PSQI global score was 8.56 ± 3.12 (range 0–18) with 84.3% of the sailors classified as “poor sleepers” (PSQI score > 5). From the 892 sailors, 661 were watchstanders (453 in fixed watchstanding schedules, 208 in rotating) and 231 were nonwatchstanders.

Almost all sailors (817, 91.6%) reported that at least one habitability-related factor in the berthing compartment affected their sleep. The median number of habitability issues reported per sailor was 3 (IQR = 3; calculated over those sailors who reported at least one habitability concern). As shown in Table 2 and Figure 1(a), the most frequently reported group of issues was noise (557, 62.4%), followed by temperature (511, 57.3%) and poor bedding conditions (370, 41.5%). In terms of the 13 habitability issues we assessed (Table 2 and Figure 1(b)), the most frequently reported issue was ambient temperature in the berthing compartment (too hot: 416, 46.6%; too cold: 178, 20.0%), followed by noise inside berthing (352, 39.5%) and light (347, 38.9%). Two issues were reported less frequently: odors (168, 18.8%) and ship motion (121, 13.6%).

Table 2

Habitability Factors Affecting Sailor Sleep

Noise	557 (62.4%)
Noise inside berthing	352 (39.5%)
Noise by other people	318 (35.7%)
Noise outside berthing	207 (23.2%)
Public announcement system (1MC)	194 (21.8%)
Temperature	511 (57.3%)
Temperature too hot	416 (46.6%)
Temperature too cold	178 (20.0%)
Poor bedding conditions	370 (41.5%)
Mattress	269 (30.2%)
Bed size	169 (19.0%)
Pillow	130 (14.6%)
Rack curtain	91 (10.2%)
Light	347 (38.9%)
Odors	168 (18.8%)
Ship motion	121 (13.6%)

Next, multiple regression analysis was used to assess whether habitability issues were associated with sailors’ well-being in terms of daytime sleepiness (ESS scores), insomnia symptoms (ISI scores), sleep quality (PSQI global scores), mood (POMS scores), and sleep attributes (daily sleep duration, number of sleep episodes/day). Analysis was based on two groups of models. The first group included the number of habitability-related issues reported by each sailor (ranging from 0 to 13) as the potential predictor factor. Ship, gender, rank group, and occupational group were confounding factors. Results showed that increased number of reported habitability-related issues was associated with more severe insomnia symptoms (ISI; p < .001), worse sleep quality (PSQI; p < .001), and worse mood as assessed by POMS TMD (p = .007), higher tension/anxiety scores (p = .035), depression scores (p = .001), and fatigue scores (p = .006; Table 3). Of note, the greater the number of reported habitability-related issues, the more sailors slept (p = .037).

Table 3

Number of Reported Habitability Complaints as a Predictor Factor of Sailor Well-Being

Variable of Interest	Entire Model			# of Reported Habitability Issues^a
Variable of Interest	R ² Adjusted	F	p-Value	Regression Coefficient	p-Value	Partial Η ²
ESS score	0.044	3.73	.001	0.672	.012	0.01
ISI score	0.124	9.38	<.001	2.29	<.001	0.07
PSQI global score	0.133	10.2	<.001	1.62	<.001	0.08
POMS TMD^a	0.074	4.71	<.001	0.352	.007	0.01
Tension/anxiety^a	0.033	2.62	.001	0.124	.035	0.01
Depression^a	0.033	2.59	.001	0.262	.001	0.01
Anger/hostility^a	0.082	5.13	<.001	0.124	.145
Vigor	0.081	5.10	<.001	−0.659	.093
Fatigue^a	0.088	5.51	<.001	0.168	.006	0.01
Confusion/bewilderment^a	0.022	2.03	.014	0.090	.079
Daily sleep duration	0.096	5.33	<.001	0.149	.037	0.01
Sleep episodes/day^a	0.130	7.08	<.001	0.015	.090

Note. ESS = Epworth Sleepiness Scale; ISI = Insomnia Severity Index; PSQI = Pittsburgh Sleep Quality Index; POMS TMD = Profile of Mood States Total Mood Disturbance Score. ^aSquare root transformed.

The second group of models included noise, temperature, light in the berthing compartment, ship motion, poor bedding conditions, and odors as the potential predictor factors. Ship, gender, rank group, and occupational group were confounding factors in all models. As shown in Table 4, poor bedding conditions and noise were negatively associated with sailor well-being. Results from both groups of models showed that habitability problems were associated with more severe insomnia symptoms and deteriorated sleep quality. Habitability was also associated with worse mood, daytime sleepiness, and duration of daily sleep.

Table 4

Association Between Habitability Complaints and Sailor Well-Being

Variable of Interest	Entire Model				Habitability-Related Factor^b
Variable of Interest	R ² Adjusted	F	p-Value	Noise	Temperature	Light	Motion	Poor Bedding Conditions	Odors
ESS score	0.044	3.06	<.001					0.346*
ISI score	0.119	7.01	<.001	0.681***			0.430	0.877***
PSQI global score	0.122	7.19	<.001	0.548***	0.226*			0.482***
POMS TMD^a	0.072	3.68	<.001					0.199***
Tension/anxiety^a	0.029	2.01	.007
Depression^a	0.027	1.94	.010					0.116*
Anger/hostility^a	0.085	4.19	<.001					0.087	0.129*
Vigor	0.085	4.20	<.001					0.623**
Fatigue^a	0.098	4.72	<.001					0.138***
Confusion/bewilderment^a	0.016	1.57	.057
Daily sleep duration	0.114	4.86	<.001	0.150***			0.106
Sleep episodes/day^a	0.127	5.37	<.001					0.009

Note. ESS = Epworth Sleepiness Scale; ISI = Insomnia Severity Index; PSQI = Pittsburgh Sleep Quality Index; POMS TMD = Profile of Mood States Total Mood Disturbance score. Inclusion criterion: p < .1. *p < .05. **p < .01. ***p < .001. ^aSquare root transformed. ^bRegression coefficient.

To assess whether night shiftwork was associated with our variables of interest, we repeated the multiple regression analyses. Specifically, we added whether the watch schedule included night shifts as a potential predictor factor. The pattern of results presented thus far did not change.

Based on the number of habitability issues that each participant reported, sailors were classified into two groups and then compared. Specifically, the 75th percentile group with sailors reporting five or more issues affecting their sleep (239 sailors) was compared to the 25th percentile group with sailors reporting one issue or none (200 sailors). Compared to the 25th percentile group, the 75th percentile group on average was older, had more enlisted sailors, had worse mood, and had longer daily sleep duration by approximately 17 min (Table 5). Also, compared to the 25th percentile group, sailors in the 75th percentile group were more likely to report elevated daytime sleepiness (by 23%) and moderate to severe insomnia symptoms (by 145%) and to be classified as poor sleepers (21%). Of note, the two groups did not differ in terms of occupational characteristics, that is, watchstanders versus nonwatchstanders (Fisher’s exact test, p = .453), and sailors working on rotating versus fixed watchstanding schedules (Fisher’s exact test, p = .280).

Table 5

Differences Between the 25th and the 75th Percentile Groups in Terms of the Number of Reported Habitability Issues Affecting Sailor Sleep

Variable of Interest	25th Group(n = 200)	75th Group(n = 239)	p-Value	Effect Size
Age in years, MD ± IQR	24 ± 8	27 ± 7	<.001^a,c	0.179^e
Sex (males), # (%)	160 (80.0)	183 (76.6)	.418^b	–
Enlisted personnel, # (%)	164 (82.0)	214 (89.5)	.026^b,c	1.09 (1.01–1.18)^d
ESS score	9.30 ± 4.56	10.4 ± 4.64	.015^a,c	0.116^e
EDS (ESS > 10), # (%)	80 (40.0)	118 (49.4)	.054^b,c	1.23 (1.00–1.53)^d
ISI score	9.33 ± 4.65	12.7 ± 4.90	<.001^a,c	0.321^e
ISI ≥ 15^f, # (%)	28 (14.0)	82 (34.3)	<.001^b,c	2.45 (1.67–3.61)^d
PSQI global score	7.35 ± 2.94	9.83 ± 3.20	<.001^a,c	0.375^e
Poor sleeper (PSQI > 5), # (%)	151 (75.5)	218 (91.2)	<.001^b,c	1.21 (1.11–1.32)^d
POMS TMD	34.4 ± 31.0	44.9 ± 33.5	.003^a,c	0.168^e
Tension/anxiety	9.32 ± 5.72	10.8 ± 5.73	.004^a,c	0.162^e
Depression	9.58 ± 9.88	13.1 ± 11.3	.001^a,c	0.186^e
Anger/hostility	11.5 ± 8.36	13.2 ± 9.23	.117^a	–
Vigor	13.3 ± 5.86	12.5 ± 5.45	.334^a	–
Fatigue	9.74 ± 5.86	11.5 ± 5.63	.006^a,c	0.157^e
Confusion/bewilderment	7.65 ± 4.14	8.83 ± 4.72	.023^a,c	0.129^e
Daily sleep duration (hr)	6.49 ± 0.922	6.77 ± 0.895	.008^a,c	0.159^e
Sleep episodes/day, MD ± IQR	1.33 ± 0.500	1.39 ± 0.657	.248^a	–

Note. EDS = elevated daytime sleepiness; ESS = Epworth Sleepiness Scale; ISI = Insomnia Severity Index; PSQI = Pittsburgh Sleep Quality Index; POMS TMD = Profile of Mood States Total Mood Disturbance score. Scores are presented as M ± SD or as otherwise stated. ^aWilcoxon rank sum test. ^bFisher’s exact test. ^cStatistically significant according to the post hoc BH-FDR controlling procedure. ^dRelative risk (95% confidence intervals). ^eEffect size r. ^fAn ISI score of 15 or more denotes the “Clinical insomnia—moderate severity” and “Clinical insomnia—severe” categories.

Discussion

Noise from various sources (reported by ~62% of the participants), high ambient temperature (~47%), poor bedding conditions (~42%), and ambient light (~39%) were the most frequently reported factors affecting the sleep of sailors in their berthing compartments. In general, the pattern of habitability-related complaints in this study is similar to our findings from the High Speed Vessel (HSV-2) and the two variants of the Littoral Combat Ship (Matsangas & Shattuck, 2017). In agreement with earlier research, noise remains one of the most frequently reported factors contributing to sleep problems (Hansen & Holmen, 2011). However, in our sample, fewer sailors (Δ = ~20%) complained about their mattresses compared to an earlier study on USN sailors serving on various types of ships (Wilcove, 2006). This difference may be attributed to the fact that our study was explicitly focused on complaints related to sleep per se, whereas Wilcove’s study assessed habitability in relation to sailor well-being.

Most importantly, though, our results showed that habitability in the berthing areas is associated with sailor well-being. Compared to their peers with fewer complaints, sailors with more habitability-related complaints are 23% more likely to have elevated daytime sleepiness, to report insomnia symptoms (145%), and to report lower sleep quality (21%). Individuals with more complaints tend to have worse mood as measured by the POMS (increased total mood disturbance, tension/anxiety, depression, fatigue, and confusion/bewilderment scores). In terms of specific groups of factors, fewer complaints about bedding conditions and fewer complaints about noise were associated with sailor well-being.

Interestingly, sailors who expressed concerns about the habitability in their berthing compartment tended to sleep more. This finding is not surprising if we consider that, due to workload and operational/training demands, sleep at sea is often split sleep, that is, sleep is accrued in multiple episodes that may not align with the sailor’s circadian rhythm (Shattuck et al., 2018, Shattuck et al., 2019). Therefore, sailors who accrue their sleep in more sleep episodes may report worse sleep quality compared to sailors with the same (or even less) daily sleep duration accrued in fewer sleep episodes (Kleitman, 1949; Matsangas & Shattuck, 2019).

Overall, approximately 92% of the sailors who participated in our studies reported that at least one habitability-related factor in the berthing compartment was affecting their sleep. The large number of sailors reporting an issue may seem surprising given that habitability standards have existed for many decades, are continuously being revised and improved, and include provisions explicitly focusing on berthing spaces. A better look at the provisions of T9640-AC-DSP-010/HAB, however, leads to two important conclusions. First, not all of the habitability concerns we identified in our study are covered in the habitability guidelines. For example, the provisions regarding the acoustic environment do not consider crew members as a potential source of noise (e.g., noise from other people in the compartment and the use of the public announcement system). Second, even though noise and ambient light are included in T9640-AC-DSP-010/HAB, the corresponding provisions are not focused on improving sleep per se. Specifically, MIL-STD-1474E (the primary standard for the acoustic environment) notes that comfort of personnel is the primary consideration in berthing spaces and staterooms (DoD, 2015).

The same issue exists for ambient light and bunk curtains. That is, existing provisions do not address ambient light as a factor affecting sleep; in the current provisions, curtains are only considered a feature to address sailor privacy (NAVSEA, 2016). Curtains made from noise-dampening materials, however, may reduce noise in the bunk and hence improve sleep quality. T9640-AC-DSP-010/HAB provisions for berthing compartments should focus on eliminating the negative effects of noise and light on crew members’ sleep. Since the early 1990s, ANEP-25 has included a recommendation that the acoustical environment of ships should prevent interference with the crew’s sleep (NATO, 1990). Second, some noise in the berthing compartments occurs because crew members work on different schedules and consequently come and go throughout the course of the day, entering and leaving the space while other crew members are sleeping (Matsangas & Shattuck, 2017). This problem can be partially solved if berthing compartments and arrangements in new ships are designed (and in existing ships assigned, to the extent possible) according to the organizational structure of the ship. Along these lines, the Maritime Labour Convention (MLC) notes that sleeping rooms of seafarers should be arranged so that watches are separated and that seafarers working during the day do not share a room with night watchstanders (ILO, 2006).

Lastly, a comment is needed regarding ambient temperature in berthing spaces. Even though T9640-AC-DSP-010/HAB includes detailed provisions for the control of ambient temperature, approximately 57% of the sailors reported that temperature (either too hot or too cold) in the berthing space affects their sleep. The source of the ambient temperature issue is not known. Is it the effectiveness of the heating, ventilation, and air conditioning system for the climate conditions in the areas the ships operate or perhaps the location of the vents in the berthing spaces leading to less than optimal airflow? Conclusive answers cannot be provided with the data from this study. The importance of optimal temperature for good sleep (Haskell et al., 1981), however, suggests that further investigation is needed to identify why ambient temperature is considered an issue of concern by sailors.

In conclusion, habitability issues in the berthing compartments of naval ships are associated with crew sleep patterns, alertness, and mood. To our knowledge, this is the first series of studies that quantifies this association. However small, this association should be taken into consideration by ship designers. Noise from various sources, ambient temperature, poor bedding conditions, and ambient light were the most frequently reported factors of concern. Future studies should further address the detrimental effect of nonoptimal conditions in berthing compartments and crew well-being, and investigate viable and cost-effective methods to mitigate the problems that are identified.

Study Limitations

This study also has a number of limitations. The data presented from the aircraft carrier are predominantly (~93%) from sailors in the reactor department and, therefore, the opinions expressed are focused on the berthing compartments of this specific department. In contrast, the data from the cruisers and the destroyers are representative of the entire ship’s company, and therefore represent all berthing compartments in those ships. Future efforts should focus on assessing habitability-related issues in each available berthing space and identify potential problems in each compartment. Also, our list of habitability-related issues should be expanded with other factors, for example, airflow, air quality to include contaminants (odors, fuel, etc.,), ship motion, mechanical vibration, free space in the berthing compartment, and anthropometrics of bed size. Lastly, the habitability concerns in this report are all self-reported and, by definition, subjective. Even though such subjective assessments are of value, an investigation of habitability-related conditions in berthing compartments using objective methods (e.g., light, noise, and odor monitors) is important and should be included in future studies.

Key Points

Noise from various sources, ambient temperature, poor bedding conditions, and ambient light were the factors most frequently reported that affect USN sailors’ sleep in their berthing compartment.

Habitability in the berthing areas is associated with sailor well-being as measured by elevated daytime sleepiness, insomnia symptoms, sleep quality, mood, and sleep duration.

Poor bedding conditions and noise from various sources were the two major groups of factors associated with sailor well-being.

Ship designers should take our findings into consideration and investigate viable and cost-effective methods to mitigate the problems we identified.

Footnotes

Acknowledgments

The views expressed in this study are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. government.

Author(s) Note

The author(s) of this article are U.S. government employees and created the article within the scope of their employment. As a work of the U.S. federal government, the content of the article is in the public domain.

ORCID iD

Panagiotis Matsangas

Author Biographies

Panagiotis Matsangas is a lecturer in the Human Systems Integration Program at the Operations Research Department at the Naval Postgraduate School. He is a retired commander of the Hellenic Navy and received his PhD in modeling and simulation from the Naval Postgraduate School in 2013.

Nita Lewis Shattuck is a professor with a joint appointment in the Operations Research and Systems Engineering Departments at the Naval Postgraduate School. She received her PhD in behavioral science from the University of Texas, School of Public Health, in 1982.

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