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Chapter 8. Manual Materials Handling Limits. Introduction. Robotics has decreased manual labor repetitive and structured jobs mostly successful industries CATCH 22: capital investment for robots, need to be successful to get investment Unstructured jobs still manual labor

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chapter 8
Chapter 8

Manual Materials

Handling Limits

introduction
Introduction
  • Robotics has decreased manual labor
    • repetitive and structured jobs
    • mostly successful industries
      • CATCH 22: capital investment for robots, need to be successful to get investment
  • Unstructured jobs still manual labor
    • construction, assembly, equipment repair, fire fighting, police, nursing
results of 1981 niosh study
Results of 1981 NIOSH Study
  • Overexertion claimed cause ~ 60% of low back pain
  • If significant lost time, <33% with back pain return to previous work
  • Overexertion injuries account for ~25% of all reported occupational injuries in the US (some industries ~ 50%)
    • ~ 66% of overexertion claims involved lifting
    • ~ 20% pushing or pulling
factors affecting manual material handling system
Factors affecting manual material handling system
  • Worker characteristics (Individual)
    • Physical: age, anthropometrics, posture
    • Sensory: visual, audit, tactile, proprio etc
    • Motor: strength, ROM, endurance
    • Psychomotor: coordination, RT
    • Personality: job satisfaction, SES
    • Training/experience: education
    • Health status: previous, drug use
    • Leisure time activities: 2nd job, sedentary
factors affecting manual material handling system5
Factors affecting manual material handling system
  • Material/container characteristics (Task & Environment).
    • Load.
    • Dimensions.
    • Distribution of load
      • 1 vs 2 hand, Moment Arm about back
    • Couplings (handles).
    • Stability of load (liquids & bulks).
factors affecting manual material handling system6
Factors affecting manual material handling system
  • Task & workplace characteristics (environment)
    • Workplace geometry
    • Frequency/duration/pace.
    • Complexity
    • environment: temperature, noise
factors affecting manual material handling system7
Factors affecting manual material handling system
  • Work practice characteristics
    • individual: speed and accuracy
    • Organization: teamwork, safety functions, medical staff
    • Administrative: safety incentives, work shift length, rotation, personal protective devices
3 strategies to prevent overexertion injury
3 strategies to preventoverexertion injury

1) design the task for all workers

2) select workers believed to be at low risk

3) train workers to reduce personal risk levels

Often determined by

socio-legal-economic considerations

lifting limits in manual handling
Lifting Limits in Manual Handling
  • Setting “safe” limits for employees
    • “gold standard” for workplace
  • Needs to consider
    • Epidemiology/etiology of MS injury
    • Biomechanical concepts
    • Physiological principles
    • Psychophysical lifting limits
lifting limits in manual handling11
Lifting Limits in Manual Handling

Note different limiting factors

1981 niosh equation to evaluate sagittal plane lifting
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • Recommendations:
    • lifting smooth, with no sudden acceleration
    • objects of moderate width (hand separation of less than 75 cm (29.5 inches)
    • Good couplings (secure handholds and low foot slippage potential)
    • Favourable temperatures for lifting
1981 niosh equation to evaluate sagittal plane lifting13
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • Need to define 4 job attributes
    • location of CofM (or handgrip center) of the object in horizontal direction (H)
      • horizontally from midpoint of ankles
1981 niosh equation to evaluate sagittal plane lifting14
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • Need to define 4 job attributes
    • location of CofM (or handgrip center) of the object in horizontal direction(H)
    • location of CofM(or handgrip center) in vertical direction at start of lift (V)
      • from floor to CofM or handle
1981 niosh equation to evaluate sagittal plane lifting15
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • Need to define 4 job attributes
    • location of CofM (or handgrip center) of the object in horizontal direction(H)
    • location of CofM(or handgrip center) in vertical direction at start of lift (V)
    • vertical travel distance of the hands (D)
      • from origin to destination
1981 niosh equation to evaluate sagittal plane lifting16
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • Need to define 4 job attributes
    • location of CofM (or handgrip center) of the object in horizontal direction(H)
    • location of CofM(or handgrip center) in vertical direction at start of lift (V)
    • vertical travel distance of the hands (D)
    • Frequency of lifting (lifts / minute) averaged over a period (F)
1981 niosh equation to evaluate sagittal plane lifting17
1981: NIOSH equation to evaluate sagittal plane lifting
  • objective method to determine safe load
  • BUT
    • limited to sagittal plane
    • did not consider asymmetry
    • needs more consideration of width (H)
    • needed consideration of quality of coupling
    • needed revision of weight limits based on frequency
1991 committee to revise 1994 published revision
1991 committee to revise:1994 published revision
  • considered new research findings
    • biomechanical criteria
    • physiological criteria
    • psychophysical criteria
  • added
    • angle of asymmetry from sag plane (A)
    • quality of coupling (C) in 3 classes
  • still many unknowns and controversies
biomechanical criteria
Biomechanical criteria
  • Site of greatest stress: L5/S1
  • Compressive force: critical determinant
    • 3.4 kN (3400 Newtons)
      • safe for most but not all employees
      • cadaver study & biomechanical models
spinal motion segment failure
Spinal Motion Segment Failure

Traditional

Model

Revised

Model

(McGill, 1997)

physiological criteria

Fatigue, by Rodin

Physiological criteria
  • energy expenditure related to repetitive lifting
  • large energy expenditures required to lift the body and the load
  • if lifting energy requirements exceed energy producing capacity==>fatigue
psychophysical criteria
Psychophysical criteria
  • how much an individual will choose to lift if given the choice when lifting for an extended period of time
  • Guidelines set to meet acceptable lifting capacity of 75% of females (99% males)
quantifies risk increase when
Quantifies risk increase when:

1. Heavy objects are lifted.

2. The object is bulky.

3. The object is lifted from the floor.

4. Objects are frequently lifted.

5. Poor grips are provided

revised 1994 niosh lifting equation
Revised (1994) NIOSH lifting equation

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

RWL: Recommended weight limit

Identifies the MAXIMAL load for the scenario defined in the

equation. Use this value to calculate level of stress.

Lift Index (LI): Task load / RWL

: percentage of healthy population at risk???

: most healthy population can exceed LI of 1.00??

Compare relative hazard of two tasks/two environments

If LI > 3 many workers at elevated risk

revised 1994 niosh lifting equation25
Revised (1994) NIOSH lifting equation

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

RWL: Recommended weight limit

Identifies the MAXIMAL load for the scenario defined in the

equation.Use this value to calculate level of stress.

Lift Index (LI): Task load / RWL

: percentage of healthy population at risk???

: most healthy population can exceed LI of 1.00??

Compare relative hazard of two tasks/two environments

If LI < 1 protective of most workers

revised 1994 niosh lifting equation26
Revised (1994) NIOSH lifting equation

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

LC: Load constant

Maximum recommended weight for lifting at the standard

lifting location

sagittal plane, occasional lift, good couplings,

<25 cm vertical displacement

23 kg (230N) or 51 lbs

acceptable to 75% of female population

revised 1994 niosh lifting equation27
Revised (1994) NIOSH lifting equation

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

Multipliers used to adjust (reduce) the recommended

load to compensate for less than optimal lifting conditions

revised 1994 niosh lifting equation28
Revised (1994) NIOSH lifting equation

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

Horizontal multiplier: increased horizontal distance from spine

increases moment arm and leads to increased lumbar stress.

HM (metric) = 25 / H

HM (english) = 10/ H

H: horizontal distance of hands from midpoint between ankles

Note that 25 cm (10 in) is about width of body.

Measured at origin and destination.

revised 1994 niosh lifting equation29
Revised (1994) NIOSH lifting equation

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

Vertical multiplier: reflects increased lumbar stress lifting loads

near the floor (What is the cause??)

Lifting from near floor requires greater energy expenditure (Why?)

Therefore reduce RWL by 22.5% if lift begins at floor

More dangerous to lift load to or past shoulder height

Therefore reduce RWL by 22.5% for shoulder height

VM = (1-0.003 |V-75|) V in cm

VM = (1-0.0075|V-30|) V in inches

where V is vertical distance of hands from floor

Measure at origin & destination, use worst case

revised 1994 niosh lifting equation30
Revised (1994) NIOSH lifting equation

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

DM: Distance multiplier

reflects increase in physiological demand as

vertical distance traveled is increased ( fatigue)

DM = (0.82 + (4.5 / D ) in cm

DM = (0.82 + (1.8/ D) in inches

where D is the total vertical distance moved

between origin and destination

revised 1994 niosh lifting equation31
Revised (1994) NIOSH lifting equation

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

Asymmetric multiplier:

lifting away from sagittal plane

Reduce load by 30% for 90 degrees of twist

AM = ( 1 - (0.0032 A))

Where A is angle of asymmetry (angular displacement from the

sagittal plane)

Measure at origin & destination, use worst case

revised 1994 niosh lifting equation32
Revised (1994) NIOSH lifting equation

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

FM = Frequency Multiplier

Table D-5, p 561 from text

Based on work duration (<=1 hr, <= 2hr, <= 8hr)

and V (vertical distance of hands from floor, in cm)

and Frequency (rate of lifting) lifts/min

revised 1994 niosh lifting equation34
Revised (1994) NIOSH lifting equation

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

CM =Coupling Multiplier

Table D-7, p562 from text

Based on V (vertical distance of hands from floor, in cm)

and quality of coupling

Note: penalty is not more than 10% decrease in RWL,

so rating not that critical.

revised 1994 niosh lifting equation35
Revised (1994) NIOSH lifting equation

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

CM =Coupling Multiplier

Table D-7, p562 from text

Based on V (vertical distance of hands from floor, in cm)

and quality of coupling

Note: penalty is not more than 10% decrease in RWL,

so rating not that critical.

calculate rwl then what
Calculate RWL, then what??
  • Calculate the Lift Index (LI), as Actual Load Lifted / RWL
  • Likely that LI > 3 poses a significant risk to many workers (<1 is protective)
  • a comparison value
    • multipliers are factors that increase stress
    • Which multiplier has greatest potential for change?
    • what changes will reduce the multipliers?
solve for the overhead
Solve for the overhead
  • 200 Newton load
  • 38 cm handles above ground
  • Ht to press of 160 cm
  • Assume steps forward the 53 cm to press
  • Work duration 8 hours
  • Loads twice during shift
  • Good grips on stock
  • Calculate
solve for the overhead38
Solve for the overhead
  • What if poor handles?
  • What if unable to step forward, so all is reach?
  • What if twists 30 degrees to load?
limitations of equation
Limitations of equation
  • Does not recognize individual risk assessment
    • future include age, sex & Body weight???
  • Not for use with one-handed lifting
    • or seated, or kneeling, or constrained, or hot/cold/contaminated environment, or shovel use, or high-speed lifting
  • Physiological criteria relate to whole body fatigue, not site specific
    • relates more to risk of injury?
summary
Summary
  • Provides a quantitative starting point for comparing tasks.
  • Links factors associated with risk of LBP in a multiplicative manner
  • Starting point for ongoing research and validation of assumptions and guidelines
homework
Homework

Go to this website by Dr. Peter Keir (York University, Toronto, Canada) and do the assignment (skip the Mital calculations)

niosh recommendations to control lifting hazards
NIOSH recommendations to control lifting hazards:

Develop engineering controls such as:

  • a. Use of manual handling devices.
  • b. Repackaging load to reduce weights.
  • c. Rearranging workplace / redesign hardware to reduce H, V, & D factors.
niosh recommendations to control lifting hazards45
NIOSH recommendations to control lifting hazards:
  • Identify jobs with high musculo-skeletal injury incidence and severity rates by statistical analysis of medical data.
niosh recommendations to control lifting hazards46
NIOSH recommendations to control lifting hazards:
  • Observe suspect jobs and for each lift task measure the weight of loads and related H, V, and D data, and note whether lifts are occasional or performed regularly throughout the shift.
niosh recommendations to control lifting hazards49
NIOSH recommendations to control lifting hazards:

Propose administrative controls:

  • a.Add personnel to reduce lift frequency
  • b. Use or modify job rotation to shorten the period of lifting (cross-training)
    • rotate workers onto other, less physically demanding jobs
niosh recommendations to control lifting hazards50
NIOSH recommendations to control lifting hazards:
  • Develop formal training programs emphasizing lift techniques that minimize H, V, D, & F
niosh recommendations to control lifting hazards51
NIOSH recommendations to control lifting hazards:
  • Develop worker selection & placement procedures to improve match between worker physical work capacities and specific lifting requirements in problems jobs.
niosh recommendations to control lifting hazards52
NIOSH recommendations to control lifting hazards:
  • Implement the most feasible solutions and evaluate effectiveness with follow-up medical and job surveillance.
load pushing and pulling capabilities
Load Pushing and Pulling Capabilities:
  • Approximately 20% of overexertion injuries have been associated with pushing and pulling acts.
  • One of the leading causes of non-vehicle related deaths in industry is slipping and/or falling.
load pushing and pulling capabilities54
Load Pushing and Pulling Capabilities:
  • Vertical height of the handle is critical
    • About hip height is recommended.
      • vision
      • strength in this position
      • allows development of horizontal force without compromising friction
material handling considerations
Material Handling Considerations
  • Stand/sit erect
  • Eliminate reaches
  • Use rollers/conveyors vs. carriers/pivots
  • Gravity-fed slides/shelves
  • Keep it close to worker
  • Tilt bins
  • Allow access to all sides
low back pain and lifting
Low back pain and Lifting

Study: Training Won't Prevent Back Injuries

February 2, 2008

Training showing the correct way to lift heavy objects does not prevent back injuries, according to a systematic review published on the Web site of the BMJ (British Medical Journal).

Back pain is a highly prevalent complaint and a cause of much suffering. In the UK, employers have to ensure workers get proper training on how to handle loads correctly and this generally includes advising workers on specific lifting techniques. However this study, which reviewed all the evidence currently available, found no evidence that the advice has any effect.

The researchers looked at 11 studies: eight studies dealt with health workers who manually handled patients, the other three looked at baggage handlers and postal workers. All the participants in the studies worked in jobs where there was strain on the back and where there was the potential for alleviating any strain through an intervention such as training. None of the workers in the studies were actively seeking treatment for back pain.

The researchers found no difference in back pain in studies where one group received training and the other didn’t. Training compared to minor advice (a video) showed no effect on back pain after a year.

Another trial showed no significant difference in back pain between one group who received training and another who were given back belts to wear. Training and physical exercise were compared in one trial and again no difference in back pain was found during a follow up less than a year later.

Finally a group receiving both training and an assistive device was compared to a group receiving training only and another control group which received nothing -- there was no difference in back pain at follow up.

The researchers say either the advocated techniques do not actually reduce the risk of back injury, or workers do not significantly change their habits enough for it to make any difference.

They concluded that what's needed is a better understanding of the relationship between exposure to stresses on the back at work and the subsequent development of back pain in order to develop new and innovative ways of preventing back pain because of lifting.

In an accompanying editorial, Associate Professor Niels Wedderkopp says the current advice for people with back pain to stay active may not be appropriate for people whose work involves heavy lifting. He stated: "A change of job and (prudently) staying active in daily life may be the best way for these patients to regain command of their back and their occupation."

http://www.ohsonline.com/articles/58040