Health Hazard Assessment
Hazard Category - Musculoskeletal Trauma 


LIFT AND CARRY

Data Requirements and Initial Recommendations.
(1) Determine the weights and lift requirements (e.g. mechanical or multi-Soldier lift) and include warning labels with those weight and lift/carry requirements to the applicable components and in the technical manuals (TM).   

(2) Provide data for analysis as identified on the Health Hazard Assessment Lifting Analysis Worksheet (Enclosure 1) to support the completion of a definitive HHA on this potential health hazard concern.   

(3) Apply the design guidance for efficient handling contained in Military Standard (MIL-STD) 1472G paragraph 5.8.6.3 and 5.9.11 (reference 1) to the materiel design to the maximum extent feasible.  Place emphasis on heavy items that require manual lift/adjustment.    

Health Effects.
A potential source of exposure to musculoskeletal trauma is the lift/carry of heavy components or equipment.  Some components may require multiple personnel to lift, carry, and/or install.  Manual handling and lifting are a major cause of work-related lower back pain (LBP) and impairment and shoulder or arm pain.  The LBP can occur by direct trauma, a single exertion (overexertion), or as a result of multiple exertions (repetitive trauma).  The LBP and impairment are also associated with other work-related factors such as pushing and pulling activities, extreme postures such as forward flexion, and cyclic loading. 
  
Medical Criteria.
(1) The MIL-STD-1472G paragraph 5.8.6.3 (reference 1) contains design guidance for efficient handling.  Lifting limits or the maximum values in determining the design weight of items required for one or multiple-Soldier lifting is included.  There is also information presented regarding lifter interference with one another, lift frequency, lift height, lift load size, carrying limits, object carry size, mixed gender lift and carry, labels, handles and grasp areas, and push and pull forces.  Each of these should be considered when requiring Soldiers to perform lift, carry, and push and pull tasks during use of the materiel and its components. 

(2) Each item required to be manually lifted/carried should be labeled with their weight and lifting requirements according to MIL-STD-1472G, paragraph 5.8.6.3.12.  Where mechanical or power lift is required, hoist and lift points shall be provided and clearly labeled.  All lift and carry information should be included in the TMs.    

References.
(1) Military Standard (MIL-STD) 1472G, Department of Defense Design Criteria Standard – Human Engineering, 11 Jan 12.

WHOLE-BODY VIBRATION

Data Requirements and Initial Recommendations.
(1) Collect whole-body vibration (WBV) test data in accordance with the guidance cited in International Organization for Standardization documents (references 1 and 2).  Provide WBV test data for the materiel to the U.S. Army Institute for Public Health, Ergonomics Program, reported in the British Columbia Research (BCR) format so that a definitive health hazard assessment can be completed (see example below). 

(2) Eliminate or control exposures to WBV by design to the maximum extent feasible.      

Health Effects.
Personnel operating and riding materiel may be subjected to excessive WBV during prolonged use or movement even at low speeds over improved terrain.  The health effects associated with exposure to WBV include herniated and degenerative lumbar disc disease and low back pain.  A number of engineering controls/design features are available to reduce or control Soldier exposures to WBV (e.g. seat padding/suspension, vehicle suspension) and should be applied to the maximum extent feasible to the design.     
  
Medical Criteria.
To minimize the effects of whole body vibration from vehicles on health, the root-mean square value of the frequency-weighted translational accelerations should not exceed the health guidance cautions defined by ISO 2631-1 Annex B (reference 1).  If possible, exposure within the health guidance caution zone should be avoided.  Frequencies below 20 hertz (Hz), where major body resonances occur, should be avoided.  To preclude impairment of visual tasks, vibration between 20 Hz and 70 Hz should be minimized.  The transmission of higher frequency vibration through any seating systems should also be minimized, especially where the body or head come in contact with the seatback or headrest. 

References.
(1) International Organization for Standardization (ISO) 2631-1, Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole-body Vibration Part 1: General Requirements, 1997.

(2) International Organization for Standardization (ISO) 2631-5, Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole-body Vibration Part 5: Method for Evaluation of Vibration Containing Multiple Shocks, 2004. 

Supplemental References.
(1) Military Standard (MIL-STD) 1472F, Department of Defense Design Criteria Standard, Human Engineering, 23 Aug 99.

BCR Test Data Format Example

 BCR Test Data Format Example

Image Source:  U.S. Army Public Health Command, Ergonomics Program, 2011

SEGMENTAL (HAND-ARM) VIBRATION

Data Requirements and Initial Recommendations.
(1) Provide data regarding the tool type, manufacturer, acceleration (m/s2), frequency (Hz), and use scenarios for each piece of equipment. 

(2) To minimize the effects of hand-arm vibration on health, the root mean square value of the frequency-weighted translational accelerations shall not exceed the health guidance caution zones for the expected daily exposures defined by American National Standards Institute (ANSI) S2.70.  If possible, exposure within the health guidance caution zone (>2.5 m/s2) shall be avoided.

(3) Ensure workers exposed to continuous hand-arm vibration (HAV) take a 10-minute break each hour.  Place an advisory to this effect in the equipment user manuals.

(4) Ensure an advisory is placed in the equipment user manuals to issue Soldiers anti-vibration gloves.  Where protective equipment is used to reduce personnel exposures, only full finger gloves, certified by a third party as meeting anti-vibration criteria in accordance with ANSI S2.73/International Standard Organization (ISO) 10819 may be used.

(5) Place an advisory in equipment user manuals for workers to keep hands warm and dry while using vibration power tools.

Health Effects.
Hand-arm vibration is associated with such illnesses as carpal tunnel syndrome, Reynaud’s phenomenon and Hand-arm Vibration Syndrome (HAVS).  The HAV is usually transmitted through equipment that a worker uses.  Exposure to HAV over many years may cause decreased hand muscle strength, and may cause numbness or cold sensitivity.  Several factors increase the risk of injury: vibration frequency, vibration magnitude (acceleration), exposure time, temperature, and tool design. 
  
Medical Criteria.
The ANSI provides exposure limit values for the control of hand-arm vibrations.  Although adherence to the exposure limit values alone does not guarantee the control of HAVS, they provide a nationally recognized standard to base comparisons of exposure data.

ANSI Vibration Exposure Time

  Segmental (hand-arm) Vibration Exposure. Source: ANSI S2.70-2006 

                                                                 Image Source: ANSI S2.70-2006

References.
(1) Guide for the Measurement and Evaluation of Human Exposure to Vibration Transmitted to the Hand, ANSI S2.70-2006, Acoustical Society of America, Melville, NY.

(2) Mechanical vibration and shock - Hand-arm vibration - Method for the measurement and evaluation of the vibration transmissibility of gloves at the palm of the hand, ANSI S2.73-2002 (R 2007)/ISO 10819:1996, Acoustical Society of America, Melville, NY.

 

HEAD SUPPORTED MASS

Data Requirements and Initial Recommendations.
(1) Provide the weight of the head supported mass (HSM), a measure of load asymmetry imposed by the HSM along the x and z axes, and any acceleration/deceleration forces associated with the activities where the materiel will be used.

(2) Disperse the weight so load is distributed more evenly over the head and its gravitational axis.

(3) No additional devices should be attached to the helmet during parachute operations.            

(4) If materiel is used when sitting, ensure chairs are equipped with posterior head/neck support that can be adjusted so that wearers can achieve proper head-on-neck alignment.

(5) Enforce administrative controls that provide users with periodic rest periods.  During this rest period, the materiel should be removed.  Provide users with instructions on postural alignment and exercises that may provide temporal relief from biomechanical stress.

Health Effects.
Devices that increase the weight supported by the Soldier’s head and neck will possibly shift the center of head-supported mass off the centerline, placing the user at risk of acute and chronic neck injury and degraded performance.
  
Medical Criteria.
Currently approved damage risk criteria are not available for health hazards associated with head-supported devices.  Medical and safety personnel, specifically the U.S. Army Aeromedical Research Laboratory (USAARL), are currently working to develop damage risk criteria for head-supported devices. If discomfort develops in vibration environments when the material is attached and deployed, Soldiers should be advised to either stow or remove the item from the helmet unless operational conditions dictate otherwise. Unless operational conditions dictate otherwise, Soldiers riding on military vehicles should be advised to remove helmet-mounted devices to reduce the risk of acute neck injury if the vehicle is involved in an accident.  Soldiers should continue to wear the basic helmet for its blunt and ballistic impact protection.



SHOCK (ACCELERATION/DECELERATION)

Definition.
Mechanical shock is a sudden acceleration or deceleration that transmits an abrupt force from a point of contact on the Soldier’s body to some other object.  The entity making contact with the Soldier may be an item of equipment, an article of clothing or the environment.

Data Requirements and Initial Recommendations.
The Army Institute of Public Health has not established data requirements for assessing mechanical shock from acceleration/deceleration.  It is anticipated that data requirements will include a method to measure acceleration either directly from an accelerometer or indirectly through calculation.  Since most jolt exposures occur while the body is in intimate contact with equipment it may also be necessary to use a force gage to measure forces transmitted to the body at those contact locations.

Recommendations to mitigate the mechanical shock from acceleration/deceleration depend upon the design of the equipment involved with the exposure.  Typical recommendations may include implementing interventions to control the rate of velocity change or alter the forces transmitted through contact points with the human.  Forces at contact locations may be moderated by increasing the surface area of the contact, adding cushioning or incorporating a harness or suspension.

This assessment, like other musculoskeletal assessments, will employ a systems approach. Exposure to mechanical shock will be evaluated within the context of the other items in the Soldier’s ensemble that are required to be worn.  In other words, the Soldier, uniform, personal protective equipment and other equipment carried on his/her person will be assessed as a unitary system that considers the interactions between all components.  Therefore, assessment of mechanical shock will also require a description of all system components including personal protective equipment, clothing and other equipment.

Health Effects.
Exposure to mechanical shock as a consequence of customary interactions with equipment or the environment can result in a range of injuries from minor soft tissue damage to death.

Exposures to low levels of mechanical shock may simply cause pain or clinically insignificant injury.  However, repeated exposures to low levels of mechanical shock may also yield cumulative trauma that could impair function over time.  Moderate levels of mechanical force often produce pain, superficial ecchymosis or deep tissue hematoma at contact locations.  Exposures to high levels of mechanical shock increases the depth of penetration and the likelihood of injury to a critical organ.  More severe injuries include (but are not limited to) sprains, fractures, dislocations, visceral damage, nerve injury and head trauma.

Medical Criteria.
Numerous biomechanical studies provide useful insights into the amount of mechanical shock that specific human tissues tolerate.  Since most studies have either been conducted on cadavers or, most commonly, on isolated anatomical specimens, the data is often difficult to apply to the types of exposures encountered in dynamic military work environments.  This is due to the fact that mechanical shock interacts differently with intact, living subjects than with tissues studied in isolation.  Caution should be observed when applying biomechanical injury criteria to military operations to ensure similarity between the research conditions and the military operation being targeted.

Example:  Assessing Shock from Parachute Use.
Assume that an analysis of the potentially adverse mechanical exposures of a parachute is being conducted.  A preliminary task analysis reveals three opportunities for exposure that may negatively impact the health of musculoskeletal tissues:  load bearing, parachute deployment and parachute fall landing (PFL).

Parachute Load Bearing.  Personnel will need to doff, don and wear the parachute.  Since this task does not include exposure to mechanical shock it will not be discussed in this section.  This form of mechanical stress requires a separate analysis.

Parachute Deployment.  Parachute deployment subjects personnel to mechanical stress.  After jumping from the plane the paratrooper accelerates during the fall.  Typically the magnitude of this acceleration is below the injury threshold and not significant enough to merit assessment.  However, the abrupt decrease in acceleration that occurs after the chute opens transmits a profound jerk through the axial skeleton.  The magnitude of this force should be assessed to determine risk of thoracic and lumbar spine injury.  The body’s reaction to the jerk from canopy opening includes rapid, forceful head and neck motion. The health effects of this reaction should be analyzed using a head supported mass model that considers the weight of the helmet that is required wear.

Parachute Landing Fall (PLF).  Since rate of acceleration during the fall is strongly influenced by parachute design the health effects of the ground reaction force when the paratrooper impacts the ground should also be assessed.  The assessment should assume the paratroopers weight along with the weight of the other equipment that the paratrooper is required to wear for the mission.  For a standard Health Hazard Assessment, nominal wind speed and weather conditions should be assumed.  In addition, the modeling should assume that the paratrooper uses proper PLF technique.  In other words, the assessment of the parachute should not be penalized by improper user technique that increases the probability of adventitious injury.

References.
(1) Crowell HP, Treadwell TA, Faughn JA, et al.  Lower Extremity Assistance for Parachutist (LEAP) Program: Quantification of the Biomechanics of the Parachute Landing Fall and Implications for a Device to Prevent Injuries, Army Research Laboratory, AL-TR-926, November 1995.

(2) Filipovic N, Vulovic R, Peulic A, et al.  Noninvasive determination of knee cartilage deformation during jumping, Journal of Sports Science and Medicine, 8:584-90, 2009.

(3) Khader GA and Huston RL. Analysis of opening shock of a chest mounted reserve parachute J Biomech Eng 109(2):121-5, 1987.

(4) Makela JP and Hietaniemi K. Neck injury after repeated flexions due to parachuting, Aviation, Space, and Environmental medicine, 68(3):228-9, 1997.



RECOIL (SHOULDER-FIRED WEAPONS)

Definition.
Recoil is a specific type of mechanical shock that occurs when the reactive force from discharge of a firearm propels the weapon backwards and imparts mechanical force to the point of contact with the Soldier’s body.  The magnitude of recoil force delivered to the user is dependent upon several factors including the design of the weapon as well as firing technique.

Data Requirements and Initial Recommendations.
Data requirements for recoil are currently being developed.  It is anticipated that data requirements will necessitate conducting a weapon kinetics study, similar to that described in TOP 3-2-045.  Specific data items required to assess the risk of musculoskeletal injury from recoil will likely include measurements of weapon acceleration, weapon speed, and displacement along the axis of the weapon that aligns with the anatomical point of contact with the operator.  In addition, the data items described in TOP 3-2-504 to calculate recoil energy will be needed: weight of gun, weight of propellant, and weight of bullet.  Information about the mission scenario will also be needed including a description of the intended operators (gender), the anticipated number of rounds that may be fired on a typical training day, the duration of training and the total number of rounds that will be fired on a training activity.

This assessment, like other musculoskeletal assessments, will employ a systems approach. Exposure to recoil force will be evaluated within the context of the other items in the Soldier’s ensemble.  In other words, the Soldier, uniform, personal protective equipment and other equipment carried on his/her person will be assessed as a unitary system that considers the interactions between all components.  Therefore, recoil assessment will also require a description of wearable items such as individual body armor.  Finally, since firing technique influences recoil transmission, a description of how the weapon is held and of firing postures will be needed.

Until specific medical criteria dictate otherwise, initial recommendations to mitigate injury include enforcing the firing limitations described in Table 1, TOP 3-2-504.  This includes limiting exposures from shoulder fired weapons to less than 60 ft-lbs of recoil force.

Health Effects.
Exposures to mechanical recoil force that occur as a consequence of normal use of a weapon can result in soft tissue injury such as contusion or laceration.  High dosages of force directed at the anterior shoulder may also produce tendonitis, focal bursitis, nerve injury or fracture of the clavicle.  Due to the fact that there is little opportunity to alter the anatomical contact point with a shoulder-fired weapon, repeated exposures may increase the probability and/or severity of operator injury.  Common symptoms of injury include pain, superficial ecchymosis or deep tissue hematoma; whereas, signs of injury include pain, minor reduction in active range of motion of the shoulder, or slight decrement in lifting capacity probably secondary to trauma of the anterior shoulder tissues.

Medical Criteria.
Currently no medical criteria have been identified for recoil exposures.  Personal factors that increase susceptibility to injury include the thickness of soft tissues (particularly the thickness of the pectoral muscles overlying the more vulnerable soft tissues in the pocket of the shoulder).  Therefore, anthropometrically smaller individuals with ectomorphic body types are at higher risk of injury.  TOP 3-2-504 contains the following design standards for recommended firing limitations for test weapons:

Firing Limitations for Test Weapons
 

Computed Recoil Energy

Limitations on Rounds

Less than 15 ft-lb (20.3 joules)

Unlimited firing

15 to 30 ft-lb (20.3 to 40.7 joules)

200 rounds/day/man

30 to 45 ft-lb (40.7 to 61.0 joules)

100 rounds/day/man

45 to 60 ft-lb (61.0 to 81.4 joules)

25 rounds/day/man

Greater than 60 ft-lb (81.4 joules)

No shoulder firing


The validity of these design criteria as a basis for medical criteria for health hazard assessments has not been substantiated.  A preliminary study conducted by Blankenship (Blankenship, et al., 2004) questioned applying the firing limits proposed by TOP 3-2-504 for the 45 to 60 ft lb range as medical criteria while shooting a shoulder fired weapon with a shoulder covered only by a uniform.  Blankenship et al. advised conducting additional studies to obtain the data needed to develop a more definitive characterization of recoil exposure.

References.
(1) TOP 3-2-504, Safety Evaluation of Hand and Shoulder Weapons, 1 March 1977.

(2) TOP 3-2-045, Small Arms - Hand and Shoulder Weapons and Machineguns, 17 September 2007.

(3) MEDICAL DEPARTMENT UNITED STATES ARMY IN WORLD WAR II. Editor in Chief: COLONEL, JAMES BOYD COATES, Jr., MC. Chapter II, Ballistic Characteristics of Wounding Agents (Maj. Ralph W. French, MAC, USA (Ret.), and Brig. Gen. George R. Callender, USA (Ret.), OFFICE OF THE SURGEON GENERAL DEPARTMENT OF THE ARMY WASHINGTON, D.C., 1962.

(4) Blankenship, Kenneth; Evans, Rachel; Allison, Stephen; Murphy, Michelle; Isome, Heath.  Shoulder-Fired Weapons with High Recoil Energy: Quantifying Injury and Shooting Performance, ARMY RESEARCH INSTITUTE OF ENVIRONMENTAL MEDICINE, NATICK, MA., MILITARY PERFORMANCE DIVISION. Accession Number: ADA425518, May 2004.