STRAIN INDEX NORA AZMI LABORATORIUM DESAIN SISTEM KERJA

STRAIN INDEX NORA AZMI LABORATORIUM DESAIN SISTEM KERJA & ERGONOMI JURUSAN TEKNIK INDUSTRI UNIVERSITAS TRISAKTI 2012

REFERENSI • Chapter 9, Handbook of Human Factors and Ergonomics Methods, in Stanton, N. et al. (eds. ) (2004) • J. Steven Moore and Arun Garg, “The Strain Index: A Proposed Method To Analyze Jobs For Risk Of Distal Upper Extremity Disorders”, American Industrial Hygiene Association Journal, 56: 443 -458 (1995).

• The strain index (SI) is a method of evaluating jobs to determine if they expose workers to increased risk of developing musculoskeletal disorders of the distal upper extremity (DUE) (Moore and Garg, 1995). • The DUE is defined as the elbow, forearm, wrist, and hand. • SI was developed, because previous exposure assessment methods were subjective, lacked standardization, and did not involve examination of risk factors' interaction.

Strain Index (SI) • The Strain Index (SI) is a score value based on a multiple of six variables • Rate 6 task variables (Table 1): – intensity of exertion (force) – – – duration of exertion (% cycle) efforts per minute wrist posture speed of work duration of task • The variables and score in the SI are derived from physiological, biomechanical, and epidemiological principles.

• According to work physiology, intensity of exertion (as a percentage of task-specific maximal effort), duration of exertion, and duration of recovery time between exertions are the critical parameters for predicting the onset and magnitude of localized muscle fatigue.

Tahapan Strain Index 1. Mengumpulkan data 6 variabel tugas yang pada SI 2. Menentukan Skala Ordinal Menggunakan Tabel Strain Index (Tabel 1) 3. Menentukan Nilai Faktor Pengali (Multiplier) menggunakan Tabel Multiplier (Tabel 2) 4. Menghitung Score Strain Index (SI) 5. Menginterpretasikan Hasil

Intensity of Exertion • An estimation of the strength required to perform the task one time. Guidelines for assigning a rating criterion are presented in the following table:

Duration of Exertion

Efforts per Minute

Hand/Wrist Posture

Speed of Work

Duration of Task • Informasi lamanya waktu bekerja diperoleh dari pekerja (perusahaan)

Menentukan Skala Ordinal Menggunakan Tabel

Menentukan Nilai Faktor Pengali (Multiplier)

Menghitung Score Strain Index (SI)

Menginterpretasikan Hasil

Keterbatasan Model SI

Contoh Kasus • Consider task with: – – – 20% MVC exertions over 60% of a cycle with 12 efforts per minute with 18˚ ulnar deviations at 95% of normal pace for a full 8 -hr shift

Quantitative Upper Limb WRMSD Risk Assessment • The example job is hazardous (13. 5>5) • Overall, SI improvement over RULA – – Considers more than basic postures Considers upper extremities Considers effort, intensity, pace Greater quantitative detail • Next step → data driven risk models

Strain Index pada Software Nex. Gen Ergonomics

SOAL Untuk pekerjaan merakit mesin pada industri manufaktur otomotif di samping ini, diketahui intensitas pengerahan tenaga cukup keras dengan durasi sekitar 35% dari total waktu pengamatan. Usaha yang dilakukan permenit mencapai 10 kali dengan kecepatan normal (fair). Pekerjaan berlangsung selama 7 jam perhari dengan postur tangan dan pergelangan tangan hampir netral. Hitunglah tingkat resiko ergonomi pekerjaan ini dengan menggunakan metode Strain Index.