Measuring Ergonomic Risk Factors: Part II of II
In Part I of this series, we discussed the risk factors of Magnitude, Repetition, Duration and Force. In Part II of II, we will be discussing: Posture and Motion, Vibration, Cold Temperatures, Work Organization and Psychosocial & Psychophysical factors.
Posture and Motion
Posture angles are measured in terms of the number of degrees a specific joint deviates from neutral.
Body landmarks for measuring angles are described in the American Academy of Orthopedic Surgeons' "Joint Motion Methods of Measuring and Recording" (1963).
Angular velocity refers to the speed at which a limb's position relative to the adjacent limb changes about an axis of rotation. Angular acceleration refers to the rate at which velocity (speed) changes about an axis of rotation.
In work situations, posture can be measured in several ways. In many cases, postures can be adequately estimated by direct observation. Observations may be estimated with videotapes, which may be played in slow motion or stopped for better viewing. Videotapes also can be used for identification of other stresses and to maintain a permanent record of the job for comparison with the job after interventions are implemented.
Manual goniometers can be used for quantitative measurement of static postures. Electrogoniometer can be calibrated in some cases to track posture for static or dynamic exertions. The accuracy and precision of electrogoniometer must be determined for each application. Their calibration should be checked each time they are used. When used with a computerized data acquisitions system, these systems can be used to track posture over a period of time.
Electromechanical goniometers, placed over a joint's axes of rotation, can be used to obtain the relative orientation (position) of the respective body segments. An electrogoniometer also can be used in conjunction with videotape to document work activities and corresponding postural angles; however, the accuracy and precision of the goniometer system must be certified. These measurements may be differentiated to obtain the angular velocity, or differentiated again to obtain the angular acceleration.
Videotaping or still photography can be used alone if the camera's line of sight is perpendicular to the planes of the measured body segment. In this case, measurements can be made directly form the videotape image. Postural angles may also be measured from a combination of video and live observations, using one to verify the other. The evaluation of awkward postures ordinarily does not require the fine detail that the foregoing techniques/instruments provide.
Measurements of the maximum amount of vibration available to the hand (e.g., "hazard level") are performed using the "basicentric" system. Hand-arm vibration measurements and analyses should be performed according to ANSI S3.34, ACGIH-TLV, and NIOSH 89-106 recommendations. As far as we are concerned, any and all vibration is hazardous.
Ambient temperature should be measured by using a thermometer. A calibrated thermistor or thermocouple can also be used to measure surface temperature readings (e.g., measuring cold exhaust of an air tool venting across the wrist).
Cold temperature magnitude is quantified in degrees Celsius. Exposure pattern is measured as the number of contacts with cold exposure pre minute, and exposure duration is quantified in minutes of exposure.
There is a large body of literature on methods of assessing work organizations and organizational stresses. There are several instruments available.