Determining Hazard Probability.

(1) Use the operational conditions (e.g., human system interactions,

environment, task information) provided by the MATDEV to determine HP. The principal assumption is that there are conditions that, if present, will complicate manual handling. These conditions increase the probability that injury could occur by causing the handler to be exposed to more biomechanical stress. Table 2–5 shows the operational

conditions that result in HP points. Further descriptions of the conditions follow. The presence of these conditions results in assignment of one or more HP points. Total the HP points to assign an HP for the system.

Table 2–5. Hazard Probability Point Assignment for Lifting and Carrying

Operational Condition Hazard Probability

Points

Team Size

1 or 2 lifters 0

3 or 4 lifters 1

>4 lifters 2

Load Symmetry Uniform load symmetry 0

Non-uniform load symmetry 1

Handles Fair to good coupling 0

Poor coupling 1

Grasp Type 2-handed lift 0

1-handed lift 1

Footing Fair to good footing 0

Poor footing 1

(a) Team size. Coordinating lift and carry efforts becomes more difficult as the number of team members increases. Lack of coordination of effort could cause shifting of the component, resulting in one or more team members accepting more than their allowable proportion of weight.

(b) Load symmetry. Components designed such that weight is not evenly distributed will cause one or more lifters to handle more than their allowable proportion of the weight. This causes them to be subjected to higher loads and more

biomechanical force, both of which can elevate risk of musculoskeletal injury. In a similar fashion, lifting symmetrical components with an odd number of lifters can result in unequal distribution of work demands among individual team members. The load symmetry points may be related to the team size points, and the recommended number of lifters may be adjusted to reduce the overall HP.

(c) Handles. As the quality of the handle declines, lifting becomes more problematic. Items that lack handholds, especially items whose shape makes them more difficult to grasp (such as cylindrical components), create additional hazards, such as slippage, or require the handler to exert more effort to hold them. Larger handles (usually >2” in diameter) cause handlers to exert more force than handles that fit the size of the handlers' hands. Small handles (e.g., ropes used as handles) tend to be very uncomfortable. Unpadded handles present similar difficulty.

(d) Grasp type. Lifting with two hands results in different weight distribution (onto that handler) than lifting with one hand. In general, one-handed lifting causes more weight to be distributed on one side of the handler's body. Although the MIL–STD–

applied to one-handed lifts. This is not a correct use of the standard. When it is clear that one-handed grasps are in use, increase the HS (reduce the amount of weight that can be lifted), or assign HP points.

(e) Footing. Handling components on non-optimal ground surfaces increases the probability of injury. Many conditions, such as uneven terrain, or negotiating ramps, steps or ladders, can reduce the quality of the ground surface. Surface conditions, such as the presence of contaminants that can decrease friction, may also contribute to risk. In addition, footing is assumed to be more difficult when handling is performed on moving surfaces or in/on a moving vehicle such as a tank, ship, or airplane. For most combat use scenarios, the footing will be difficult to characterize, and the handling will occur in less than optimal environments.

(2) Using the condition criteria described above in (1), assign and total the HP points. Use the total HP points and Table 2–6 to assign the HP level as defined in MIL– STD–882E.

Table 2–6. Hazard Probability Levels for Lifting and Carrying

Total Hazard

Probability Points Hazard Probability

≥ 4 A Frequent

3 B Probable

2 C Occasional

1 D Remote

0 E Improbable

No manual material handling

is required. F Eliminated

When assessing systems, analysts may encounter circumstances that are not covered by the conditions described in this chapter. Under such circumstances, the SME is authorized to assign additional HP points to adjust the assessment. Situations that may require such an adjustment include environments in which Soldiers must wear

additional gear or are exposed to extreme cold or temperate conditions that elevate the risk of injury.

Exposure to any biomechanical stress from lifting and carrying should be assumed to carry a potential injury risk that would prevent assigning HP F (Eliminated). However, HP F may be assigned if the exposure is eliminated. For example, if the entire handling process is mechanized, the initial HP may be reduced to a residual HP F. Employing a machine to assist with lifting, lowering, or transporting a load does not eliminate risk if the user is required to handle the load in order to use the machine. For example,

providing a conveyor to move an item does not eliminate injury risk if users are required to load/unload the item to/from the conveyor.

For the purposes of HHA, there are exposures that are not evaluated because the weight lifted is presumed to not meet the threshold for a potential injury. For example, when Soldiers are exposed to biomechanical stress from lifting and carrying

components weighing less than 31 lbs, those components do not meet the criteria for assessment.