Boat operations have been a staple of the Coast Guard’s daily duties throughout its history. Today, with the growing emphasis on missions such as homeland security, it needs ever-faster boats to run these operations quickly and safely. Yet these high-speed missions have led to an increase in a little-known hazard called whole-body vibration (WBV). Not only is WBV seldom understood by the individuals exposed to it, but more than 69 percent of safety and health professionals have little to no knowledge of how to recognize, anticipate, or control a hazard that has significant pathological, physiological, and psychological health effects.1
What the Science Shows
While in graduate school I studied WBV effects on the crew of one of the Coast Guard’s newest boats, the 45-foot response boat medium (RBM), to determine likely exposure and reduce acute and chronic occurrence of injuries and illnesses. The RBM is an all-aluminum boat with a deep-V double-chine hull, powered by two diesel engines with waterjet propulsion. A crew of three or four typically operates the RBM at small-boat stations throughout the United States. The boat is self-righting, with a maximum speed of 42.5 knots. It has a range of approximately 250 nautical miles (nm) at 30 knots and can withstand 12-foot seas and 50-knot winds.
Measurements were taken from fore (coxswain) and aft (crew-rear) seats, using triaxial accelerometers interposed between the crewmembers’ pelvises and the seat cushions. Accelerometers measure the vibration magnitude in meters per second squared in the x, y, and z axes. Measurements were taken during best-case environmental and exposure conditions—sunny, 65 degrees Fahrenheit, winds averaging 5 miles per hour (mph), and calm seas. The measurements were also taken in the following operating conditions: engine idle; transiting (6 knots); normal operating speed (30 knots); and high-speed (40 knots). The measurements were evaluated using several methods found in International Organization for Standardization (ISO) 2631-1: Mechanical Vibration and Shock—Evaluation of Human Exposure to Whole-Body Vibration, the gold standard for assessing WBV exposure.
To define exposure levels, the first step was to determine a crewmember’s likely exposure duration. This was done by interviewing Coast Guard Station Boston personnel and creating a daily minimum and maximum (worst-case) duration. The exposure durations and vibration magnitude data were compiled to calculate specific exposure values for different evaluation methods from the ISO standard.
All data pointed to the same conclusion: Coast Guard men and woman working on RBMs exceed the ISO action level, even during minimum exposure durations and, at times, likely exceed the occupational exposure limit, given that this was a best-case-scenario assessment. Figure 1 displays a standard eight-hour exposure for the coxswain at each operating condition, in each direction (x, y, z axes), and for all directions combined (vector sum). Data gathered from the crew rear-seat position showed very similar results.
WBV health effects have been well documented since the early 1960s with field, laboratory, and epidemiological data. However, few industries have been able to apply this research to better protect their workers. The effects of WBV exposure can range from annoyance and fatigue to severe back pain and musculoskeletal disorders. Unlike other physical hazards, such as noise, vibration does not attack one specific organ or part of the body. It affects the entire body to varying degrees.2 The portion of the body affected and its severity depend on the vibration magnitude, frequency, direction, duration, and even a person’s perception threshold.3
Resonance is the other important concept that affects the severity of health effects and which part of the body WBV attacks. Resonance occurs when the vibration source transmits at the same frequency as the receiver.4 For this study, the natural frequencies of specific body parts caused concern in the 0.5 to 40 Hertz range. This means negative health effects may occur in these regions of the body, and certain systems and functions can be disrupted, such as the vestibular system (the inner ear), speech, eyes, chest, head, tactile sense, depth perception, and, most important, the musculoskeletal system. WBV exposure may result in a multitude of chronic musculoskeletal disorders, including lower back pain, intervertebral disc failure, degeneration of the spine, spinal disc disease, herniated discs, local and mono lumbar syndrome, sciatica, and spondylosis (arthritis of the spine).5
Although fatigue is commonly seen as a consequence of the job, it may actually be caused by overexertion of the muscles attributed to maintaining posture—specifically, people preferring to support their bodies through their legs or other appendages during discomfort instead of using a chair—and muscle contraction during WBV exposure.6 Fatigue and other side effects, such as dizziness, sleepiness, nausea, nerve and motor disruption, blurred vision, and loss of balance, may not be worrisome health effects in isolation, but they can lead to musculoskeletal disorders as well. These side effects should also be considered risk factors in any occupational setting that could lead to a fall resulting in fractures and soft tissue injuries. Finally, the evidence shows WBV exposure also has negative psychological effects, such as anxiety and sleeplessness, and can negatively affect the nervous, cardiovascular, digestive, respiratory, and reproductive systems.7
Controlling WBV Exposure
There are several ways to control WBV exposure, although not all controls are appropriate for all workplaces. Proven control methods are shock-absorption seats, machinery and equipment maintenance, training, better work/rest balance, hull damping, speed reduction, and medical surveillance.
Some controls are not conducive to Coast Guard missions, such as reducing speed when conducting search-and-rescue operations. However, the Coast Guard does have several controls in place, including established maintenance schedules and training for machinery and equipment; limiting daily crew underway time; a medical surveillance program to monitor injuries; and shock-absorption seats on most boats. However, these are not doing enough to properly protect Coast Guard personnel.
For example, the shock-absorption seats, while modernized and a good first step to addressing vibration concerns, do not adjust to real-time changes in force or velocity. In addition, Coast Guard crew members are not trained to adjust their seats against WBV or educated on what each adjustment setting means or will protect against. Nor has the manufacturer provided adequate guidance on how or when to adjust. Hull damping is either not installed or not feasible on Coast Guard boats currently in use. Finally, there is no training to cover WBV exposure, short- and long-term health effects, and awareness, education, or personal protective equipment.
Further evaluation of WBV exposure on all Coast Guard boats is needed. This should include additional measurements and determining crew exposure durations for each boat type and unit throughout the Coast Guard. Only after exposures have been quantified can the service determine the extent of WBV exposure within its boat community and properly protect personnel. Until then, Coast Guard members in this community must understand the health effects and symptoms so they can discuss concerns with their primary care providers. This will help ensure members are properly diagnosed and protected now and in the future.
1. Helmut W. Paschold and Alexander V. Sergeev, “Whole-Body Vibration Knowledge Survey of U.S. Occupational Safety & Health Professionals,” Journal of the American Society of Safety Professionals 40, no. 3 (2009): 171.
2. Anders Kjellberg, “Psychological Aspects of Occupational Vibration,” Scandinavian Journal of Work Environment 16, no. 1 (1990): 39–43.
3. Derek R. Smith and Peter A. Leggat, “Whole-Body Vibration, Health Effects, Measurements and Minimization, Journal of the American Society of Safety Professionals 50, no. 7 (2005): 35–40.
4. Helmut W. Paschold, “Whole-Body Vibration: An Emerging Topic for the SHE Profession,” Journal of the American Society of Safety Professionals 36, no. 2 (2008): 52.
5. Helmut Seidel, “On the Relationship between Whole-Body Vibration Exposure and Spinal Health Risk,” Industrial Health 43, no. 3 (July 2005): 361–77.
6. Helmut W. Paschold and Alan G. Mayton, “Whole-Body Vibration: Building Awareness in SH&E,” Journal of the American Society of Safety Professionals 56, no. 4 (April 2011): 30–35.
7. Peter K. Halswell, Philip A. Wilson, Dominic J. Taunton, and S. Austen, “An Experimental Investigation into Whole Body Vibration Generated during the Hydroelastic Slamming of a High Speed Craft,” Ocean Engineering 126 (2016): 115–28.