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Table 1 Partial results of risk assessment

From: Pneumatically-driven stretching machine for ankle dorsiflexion: safety concepts and effectiveness test involving healthy young subjects

Hazards

Initial risk level

Solution

Final risk level

LOa

FEb

DPHc

HRd

LO

FE

DPH

HR

(a) Excessive torque is applied to the ankle, causing foot pain when the machine is working

5

5

0.5

12.5

Mechanically restrict the maximum pneumatic force (ISO 13482)

0.5

5

0.5

1.25

(b) The foot is moved more than the natural ankle range of motion when the machine is working

5

5

0.5

12.5

Use a mechanical limiter to restrict the range of motion of the machine’s moving part

0.1

5

0.5

0.25

(c) The user tries to reach a controller placed away from the body and falls, causing pain in the fixed ankle

2

5

0.5

5

Use a remote controller that can be operated by hand

0.1

5

0.5

0.25

(d) The foot is fixed in a non-relaxed posture owing to machine malfunction

1

5

0.5

2.5

Install a function to move the foot back to a relaxed posture

0.1

5

0.5

0.25

(e) The stop button does not work correctly

0.5

5

0.5

1.25

Install an emergency stop button to block the input voltage of the air-regulator

0.1

5

0.5

0.25

  1. a Likelihood of occurrence. 0: Impossible. 0.1: Almost impossible. 0.5: Highly unlikely. 1: Unlikely. 2: Possible. 5: Even chance. 8: Probable. 10: Likely. 15: Certain
  2. b Frequency of exposure to the hazard. 0.1: Rarely. 0.2: Annually. 1: Monthly. 1.5: Weekly. 2.5: Daily. 4: Hourly. 5: Constantly
  3. c Degree of possible harm. 0.1: Scratch/bruise. 0.5: Laceration/mild ill-effect. 1: Break minor bone or minor illness (temporary). 2: Break major bone or minor illness (permanent). 4: Loss of one limb/major illness (temporary). 8: Loss of two limbs/major illness (permanent). 15: Fatality
  4. d Hazard rate (HR), which is given by the product of LO, FE, and DPH. If HR is smaller than 1, the hazard is fully acceptable. If HR is smaller than 10, the hazard is judged as conditionally acceptable. Otherwise, the hazard is considered unacceptable