Sunday 12 August 2012

Ergonomic interventions for the furniture manufacturing industry


Journal - International Journal of Industrial Ergonomics
Author - Gary  A. Mirka,  Christy  Smith, Carrie  Shivers, James Taylor 

Summery
The  objectives  of  this  intervention   research  project  were  to  develop  and  evaluate  engineering  controls  for  the reduction  of low back  injury  risk in workers  in the  furniture  manufacturing industry.  An  analysis  of injury/illness records  and  survey  data  identified  upholsterers   and  workers  in  the  machine  room  as  two  occupations   within  the industry  at  elevated  risk for low back  injury.  A detailed  ergonomic  evaluation  of the activities  performed  by these workers was then performed  and the high risk subtasks  were identified. The analysis for upholsterers  revealed:

(1) High forces during the loading and unloading  of the furniture  to and from the upholstery  bucks,
(2) Static awkward postures (extreme flexion > 501; lateral bending > 201; twisting > 201) during the upholstering of the furniture.
(3) Repetitive bending and twisting  throughout the  operation.

 For  machine  room  workers,  this  ergonomic  evaluation  revealed repetitive bending and twisting (up to 5 lifts/min and sagittal flexion > 801; lateral bending > 151; twisting > 451) when getting  wooden  components   from  or  moving  them  to  the  shop  carts  that  are  used  to  transport these  materials. Engineering interventions were then developed and evaluated in the laboratory to document the reduction of exposure to these stressors.  The height-adjustable upholstery  buck system eliminated  the lifting and lowering requirements  and affected  trunk  kinematics  during  the upholstery  operation by reducing  peak  sagittal  angles by up to 79%  (average:52%; range: 27–79%), peak sagittal accelerations by up to 42% (average: 71%; range: 0–74%) and peak lateral position by up to 31% (average: 20%; range: 12–31%), and showed no impact on time to complete the task. The machine room lift reduced peak sagittal angle by up to 90% (average: 76%; range: 64–90%), peak sagittal accelerations by up to 86% (average: 72%; range: 59–86%) and had a positive impact on the time to complete the task (average reduction:  19%).





Introduction

About 75% of these establishments  are  producers  of household  furniture  making  up  88%  of  the  furniture manufacturing workforce  As with  many  manufacturing industry  sectors, the furniture  manufacturing industry has struggled with  problems  associated  with  work-related   low back   pain   and   other   musculoskeletal   illnesses. This  is  compared   to  the  incidence rates  of low back  pain  cases of private industry  as a  whole  and  for  general  manufacturing  industry.  The residential furniture manufacturing   industry   can   be  broken   into   three separate    categories:   
(1)  Upholstered   furniture (sofas,   chairs,    loveseats,   etc.), 
(2)  Case goods (tables, desks, bookshelves, dressers, etc,)
(3) Hardwood chairs (such as dining room chairs sometimes upholstered, sometimes  not).


Methods

The first step in this ergonomic intervention process  was to identify those  jobs that  posed  the greatest   risk   for   low   back   injury Incidence   and   severity  rate   data   from OSHA   Form   200  Logs  were  gathered   from   a group of 29 casegoods facilities and 11 upholstered furniture  facilities. The review of the OSHA  Log data from upholstery facilities indicated that a significant percentage  of the low back problems in these facilities were located in the upholstery department.

On-site ergonomic assessments
Fourteen different  furniture  manufacturing  facilities (both casegoods and upholstered furniture) were visited over a period of six months to conduct a high-level ergonomic  task  analysis  of the work activities performed  in these facilities. The differences in equipment  and work technique among the facilities  manufacturing  the  same  product   type were documented.

Engineering design of prototypes
The  research   and   design  team   employed   an iterative  prototyping process,  wherein  each ergo- nomic   intervention  prototype   was   subjectively evaluated  in the lab by the research  team  and  in the  field by furniture  workers  and  the  results  of these  assessments  were  used  to  improve  on  the design of the  intervention. The  principle  component of the intervention  for the upholstery  operation is a height-adjustable upholstery  buck system

Result
As was hypothesized, the height adjustability provided  by the two interventions  had a considerable impact on the trunk kinematics required to perform these simulated furniture manufacturing activities. Similarly, the results of the laboratory evaluation of the shop cart lift show consistent  improvements in   trunk   posture  as   well  as significant  changes  in the  dynamics  of  the  lifting activity. The lift also showed a significant decrease in the movement times required to perform the activity, a productivity benefit that we anticipate  will increase the likelihood that the intervention  is adopted  by the industry.

Conclusion
This paper describes two lift-assisting interventions for the furniture   manufacturing  industry. Both generated considerable  improvements  in the trunk postures and trunk kinematics required to perform  the  requisite  tasks.  Productivity benefits from these interventions  were also found,  but it is felt  that   these  productivity  improvements   may only be a fraction of those that may come from the long-term   utilization   of  these   interventions   by skilled workers attempting to maximize their productivity.

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