Ergonomic Prospective In The Land Warrior System – PASGT Helmet Design

CPT Willa R. Bobbitt, U.S. Army Center for Health Promotion and Preventive Medicine

March 1999

ABSTRACT

The Personnel Armor System for Ground Troops (PASGT) Helmet is a standard infantry helmet that provides ballistic protection from fragmenting munitions to the head, temples, ears, and neck. Originally type-classified in the late 1970’s and fielded in early 1980’s the current fielded PASGT is made of Kevlar 29® and weighs between 3.1 lbs. extra small and 4.2 lbs. extra large U.S. Army Soldier Systems Command (SSCOM), 1998. The outcome of studies related to the performance of job tasks in different environments will determine how the needs of soldiers are being met by this system. Many of the improvements and modifications made to the original design of the PASGT helmet are the results of feedback from soldiers in the field who tested the equipment. The Land Warrior IHAS system is different from the current PASGT helmet in design technology and weight, and will require intense training to ensure soldiers needs are being met.

Introduction

The IHAS uses advanced materials to provide ballistic protection at less weight than the current helmet shell. The IHAS’s helmet-mounted computer and sensor display are the soldier’s interface with the other subsystem and with the digital battlefield. Tpough the helmet-mounted display, the soldier can view computer-generated graphical data, digital map, intelligence information, and troop locations. The Night Sensor Display will integrate a helmet-mounted display with an image intensifier for access to the computer. This sensor/display assembly flips up for flexibility and electrical compatibility between day and night displays. The helmet is also designed to provide safe functioning in day and night and at nuclear, biological, and chemical environments with an inner helmet surface allowing for ventilation and deformation during impact SSCOM, 1998. The design of the IHAS does not restrict the user’s range of motion and movement of the head to any extent that would prohibit successful completion of mission – critical tasks. ®Kevlar is a registered trademark of E.I. Du Pont de Nemours & Co., Inc., Wilmington, Delaware. Use of trademarked names does not imply endorsement by the U.S. Army but is intended only to assist in identification of a specific product.

Ergonomics Evaluation Issues

Helmet Size and Weight

The weight of the helmet configured with the Land Warrior IHAS is between 3.1 lbs. and 5.4 lbs. The weight of the PASGT helmet is between 4.5 lbs. and 6.0 lbs. a difference of 6 ounces when compared to the LWS. The weight of the PASGT helmet identified a direct correlation to an increase of potential work related muscularskeletal WMSD injuries to the head and necks of soldiers during performance of functional job tasks. Soldiers’ reported during wear of the current PASGT helmet an increase of pressure on their head and that helmet was too heavy USARIEM, 1997. This chart illustrates proposed changes in the IHAS helmet weight for the LWS:

Psychophysical/ Human Factors

Psychophysical/human factors relates to a person’s ability to “rate the perceived strain” stemming from the physical work performed and to judge whether or not the strain is personally acceptable for safe performance of that task (Kromer,1997). The weight of the helmet is a potential risk factor in movements required for mission critical tasks that include the following:

Standing, kneeling, crawling, or maintaining a prone position.
Moving the head up and down and side to side.
Looking over the shoulder.
Moving of helmet during task that are specific to certain military occupational specialties (MOS 11B,11M,12B,13F,91B).
Fatigue of neck muscles during sustain wear of the IHAS helmet with equipment.

Biomechanics

Biomechanics applies to the static and dynamic effects to the soldiers’ body from vibration and impact associated with wear of the helmet. The evaluation of weight distribution and center of gravity in the helmet system helped to achieve maximum helmet comfort and to reduce neck strain. Physical demands required in MOS-specific tasks should be evaluated relative to the potential for developmentof repetitive strain disorders. The most common musculoskeletal disorder involves the neck and is associated with intervertebral disc disorders. The following table shows potential conditions identified in the International Classification of Diseases (ICD-9 Codes) related to helmet wear.

USARIEM, Technical Report 1997 (TR 97)

Antpopometry

The LWS IHAS in human body dimensions will fit the 90th percentile male and female. The design of helmet system will ensure safe and effective use by the soldier during all environmental and operational conditions U.S. Army Soldier and Biological Chemical Command (SBCOM), 1999.

Ergonomic Recommendations

The SBCOM has completed the first phase of the written for approved modification to the PASGT helmet and integration of the IHAS in the LWS. The ergonomics focus should involve identification of potential risk factors associated wear of the helmet and recommendations for reducing risks.

Although specific ergonomic risk factors have not been determined, soldiers should receive training in wear of the helmet relative to weight distribution of the helmet center of mass during job task associated with specific MOS’s identified in the table below:

Job titles identified to wear Land Warrior IHAS

USARIEM TR 97

Training should also include:

Conclusion

The outcome of studies related to the performance of job tasks in different environments will determine how the needs of soldiers are being met by this system. Many of the improvements and modifications made to the original design of the PASGT helmet are the results of feedback from soldiers in the field who tested the equipment. The Land Warrior IHAS system is different from the current PASGT helmet in design technology and weight, and will require intense training to ensure soldiers needs are being met.

References

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Individual or group training in movement over different terrain.
Fitness training in upper extremity (neck & thoracic) muscle strengthening.
Training in technical skills workload stress to reduce risk factors associated in job task performance levels i.e. ( Medical Specialist litter carry casualty lifts while maintaining proper posture of head and neck with weight of LW IHAS).
- 1-U.S Army Soldier System Command, “Personnel Armor System Ground Troops (PASGT) Helmet”, Program Manager (PM) Soldier, 1998,
- 2-Kroemer, K.H, “Ergonomic Design of Material Handling System” Screening Material Handlers. Englewood Cliffs, NJ, Prentice Hall, (6), 90-91, 1997.
- 3-Amoroso, P. and M. Yore, “Analysis of Military Occupational Specialties and Hospitalization,” U.S. Army Research Institute of Environmental Medicine (USARIEM) Technical Report (TR97), 1997.
- 4-U.S Army Soldier and Biological Chemical Command, “Fragmentation Helmet, Lightweight Marine Corps,”(USARIEM) and Natick Research Center Draft Report, 1999.

Ergonomics Working Group