Agenda Stress Workload

Stress and Workload

Definition Stress: a feeling of tension that occurs when a person assesses that a

given situation is about to exceed his or her ability to cope andconsequently will endanger his or her well-being.

Job stress: the feeling that one’s capabilities, resources, or needs donot match the demands of the job.

Acute stress: a short-term stress reaction to an immediate threat Chronic stress: a long-term stress reaction resulting from ongoing

situations

Stress

Stress

Information

Processing (IP)

Stressors

ExperienceHealth

Direct (e.g., vibration)

Physiological arousalIndirectDirect (e.g.,

lighting, noise)

Input Performance

Figure 13.1 A representation of stress effects. (Wickens et al, pg.325)

Stress Effects Produce a psychological experienceo “I hate this job/I love this job”o usually, but not always feelings of frustration

Changes in physiologyo E.g., heart rate

Affect efficiency of information processingo Attention/distractions, errorso usually, but not always degrading performance.

Stress

Stress Effects Long term negative consequences for healtho Heart diseaseo Sleep disturbanceso Difficulty in concentratingo Short tempero Job dissatisfaction

Stress

Stress Effects Direct effects

o Influence the quality of information (input) received and response (output)o Can be tolerated as long as performance is within acceptable range

Indirect effectso Influencing the efficiency of information processing

Stress

Ergonomic Stressors What are some factors

that cause stress?o EnvironmentalHeat, noise, lighting

o Physical and physiological Vibration, fatigue

o Emotional Life stress, frustration, anger

o Psychological Time pressure, threat, anxiety

Stress

Low frequency motion (rocking of a ship) andmotion sickness: acts as a distracter making ithard to concentrate. 0.3-1 Hz – motion sickness, vomiting

Physical Stressors: Motion

High frequency motion: cyclic motion (vibration) Can be specific to a part of the body (handheld power saw) or to the

whole body (driving)o Whole body vibration:

1-4 Hz – blurred vision, difficulty breathing, impaired psychomotor 4-10 Hz – chest pain, rattling jaw 8-12 Hz – backache 10-20 Hz – headache, eyestrain, speech disturbance

o Limb vibration: 40-300 Hz – pain in arm/wrist and arthritis

Physical Stressors: Motion

Psychological Stressors Perceived threat loss of esteem (i.e., potential embarrassment)

o Of something valuedo Of bodily function through injury or death

Life stress etc

Psychological Stressors

Physiological arousal (stress activates some body systems) Heart Rate Pupil Diameter Hormones (adrenaline)

Optimal level of physiological arousal Performance increases as arousal increases up to a certain point (trying

harder). Performance decreases with over-arousal (overload).

Level of Arousal

Definition The amount of work assigned to or expected from a worker in a

specified time period. Workload v.s. Stress Stress may be induced by having too much to do in too little time

o Workload level of arousal ↓ or ↑ performance Overload can result in forgetting to do some critical task

o e.g., air traffic controller forgetting that he had already scheduledanother aircraft to land on the runway.

Workload

Fatigue A physiological stressor that degrades performance and creates

problems in maintaining attentiono Due to effects of high or even moderate workload

Can be mental or physical Measureso EEG – increased alpha & theta waves, decreased betao EMG – muscle fatigue, shift of median frequency

Fatigue can also result from long periods of doing little

Workload

NASA Task Load Index Two-part Evaluation Procedure

o Ratings: 6 scaleso Pairwise Comparison: 15 pairs

Workload Scoreo Range: 0 ~ 100

Workload Assessment

NASA Task Load Index Steps

1) Collect raw rating for each scale2) Pairwise comparison3) Calculate workload score

Workload Assessment

NASA Task Load Index Steps

o Collect raw rating for each scale Put a cross mark at any vertical

tick mark that representsthe level of the workload youperceived during the task

Workload Assessment

16

X

NASA Task Load Index Steps

o Pairwise comparisonCircle the scale title that represents the more important contributor to

workload for the specific task you performed

Workload Assessment

NASA Task Load Index Steps

o Calculate workload score

Workload Assessment

X

X

X

X

X

X

NASA Task Load Index Steps

o Calculate workload score

Workload Assessment

Scales Raw Rating Weight Adjusted Rating=

(Weight × Raw)/15

Mental Demand 45 1 3.0Physical Demand 90 3 18.0Temporal Demand 30 1 2.0

Performance 65 3 13.0Effort 25 2 3.3

Frustration Level 25 5 8.3Overall Workload= (3.0+18.0+2.0+13.0+3.3+8.3)=47.7

Counts of Scale Titles selected in Step 2

Motivation 27% of all industrial injuries

670,000 injuries/yr in the United States 60% of all money spent on industrial injuries 93,000,000 lost workdays/yr

Manual Material Handling

Criteria Biomechanical

o Forces and torques of manual handlingo Effect on parts of body

Physiologicalo Energy requirements of the tasko Effect on the cardiovascular system

Psychophysicalo Combination of biomechanical and physiological stresses

Manual Material Handling

Variables in Manual Handling Individual

o E.g. age, muscle strengtho Stronger usually bettero But don’t exclude too many!

Techniqueo Training variables Posture Lift training

o People forget, fail to learn….

Manual Material Handling

Tasko E.g. object weight, ease of handling

(shape, handles, etc.), initial/final height, lift symmetry, clothing…..

o Advantage of modifying tasks to improve manual handling: Permanent change

Types of Material Handling Pushing and pullingo Better than lifting and lowering

Holdingo Static load

CarryingoWorse than pushing and pullingo Indicates poor job design

Liftingo Highly associated with low back injuries

Manual Material Handling

NIOSH Lifting Equation NIOSH: National Institute of Occupational

Safety and Health Purpose:o Rank alternativeso Identify and correct problems

Recommended Weight Limit (RWL)oRWL = LC × HM × VM × DM × AM × FM × CM

Lifting Index (LI)o LI = Load Weight / RWLo Estimated level of physical stress associated with the tasko LI>1, Hazardous job!

Manual Material Handling

RWL = LC × HM × VM × DM × AM × FM × CM

NIOSH Lifting Equation

LC: Load constant= 51 lbs HM:

o Horizontal multiplier determined by the horizontal location

o “H” (in/cm): Sagittal plane

VM:o Vertical multiplier determined by the

vertical locationo “V” (in/cm): Sagittal plane

DM:o Distance multiplier determined by

the distance moved verticallyo “D” (in/cm): Sagittal plane

AM:o Asymmetry multiplier determined by

the angular deviationo “A” (deg): Location of the load relative

to worker’s mid-sagittal plane

FM: o Frequency multiplier determined by

the lifting frequency, o F (Lifts/min)

CM:o Coupling multiplier determined by the

hand-container coupling condition.o Coupling types: Good, fair, poor

NIOSH Lifting Equation

HM= 10/H If H > 25 inches, HM=0 Computed directly or determined from

the table

NIOSH Lifting Equation

VM= 1 – 0.0075 × | V – 30 | If V>70 inches, VM=0. Computed directly or determined from

the table

NIOSH Lifting Equation

DM= 0.82 + 1.8 / D If D≤ 10 inches, DM=1.0 Computed directly or determined from

the table

NIOSH Lifting Equation

AM= 1-(0.0032 × A) Range from 0°to 135 ° If A > 135 °, AM=0 Computed directly or determined from

the table

NIOSH Lifting Equation

FM Determined from the table

o Three variables Frequency Work duration Vertical location

• V <30 inch• V≥ 30 inch

NIOSH Lifting Equation

CM Determined from the tables

NIOSH Lifting Equation

Frequency Rate <0.2 lifts/minDuration < 1 hourObject coupling: Fair

NIOSH Lifting Equation Example 1

Measures Origin Destination

ObjectWeight

40lbs 40lbs

Hand Location

Horizontal 18 in. 10 in.

Vertical 15 in. 36 in.

Vertical Distance

36-15=21 in.

Asymmetric Angle

45° 45°

H= 10 inch HM=0.56

NIOSH Lifting Equation

V= 15 inch VM=0.89

D= 21 inch DM ≈ 0.91

NIOSH Lifting Equation

A= 45° AM= 0.86

Frequency Rate <0.2 lifts/min; Duration < 1 hour; V =15 inch

FM = 1.00

NIOSH Lifting Equation

Coupling type: Fair; V= 15 inchCM= 0.95

37

Lifting Index = 2.1 (> 1.0) Hazardous job LI= Object Weight/ RWL

Note smallest multipliers HM = 0.56 AM = 0.86 VM = 0.89

Recommendations? Bring load closer to increase HM. Reduce angle to increase AM. Raise origin to increase VM.

Hazard Assessment

Does Not Apply If > 1-2 steps One-handed lifting Seated/kneeling Restricted workspace Hot/cold/contaminated objects Unexpected events (e.g., slips, falls) Unstable load Carrying, pushing, pulling Using tools (e.g., wheelbarrow) Slippery floor Unfavorable environment (e.g., hot, cold) However, sometimes used under these conditions as an approximation.

NIOSH Lifting Equation