115. Physical hazards: disorders caused by noise and vibration and their prevention

From greek.doctor
  • Disorders caused by noise
    • Humans hear from 20 – 20 000 Hz
    • Normal conversation is 60 dB
    • Chronic exposure > 85 dB may cause hearing loss
      • Higher noise causes hearing loss faster
      • High frequency sounds are more damaging than low frequency sounds
    • The phon scale
      • For the human ear and brain, not only the sound pressure level (the decibel) but also the frequency matters.
      • Unlike the normal decibel scale, the phon scale is standardized to one frequency
      • While the normal decibel scale measures sound intensity, the phon scale measures perceived sound intensity
    • Hearing loss
      • Usually occurs at 4 kHz first
      • Hearing loss is measured in decibels
      • Types
        • Temporary threshold shift
          • Recovers after 16 – 48 hours
        • Permanent threshold shift
          • Never recovers
      • Clinical features
        • Difficulty hearing words in noisy environment
        • Tinnitus
        • Need to look at person to understand words
    • Other disorders cause by noise
      • Hypertension
      • Cardiovascular disease
      • Poor cognitive performance
      • Sleep disturbance
    • Prevention
      • Primordial
        • Change environment and city structure
        • Place non-residential land between noise source and receiver
        • Place barriers between noise source and receiver
      • Primary
        • Reduce noise production
          • According to regulations, the average 8-hour noise level during a workday should be less than 80 dB
        • Increase distance between noise source and receiver
        • Use hearing protection
      • Secondary
        • Regular screening
  • Disorders caused by non-audible sounds
    • Ultrasound can kill furred animals
      • The energy is absorbed in the fur
    • Infrasound can cause headache, nausea, fatigue and hypotension
  • Disorders caused by vibration
    • Segmental vibration – vibration of a part of the body
      • Due to usage of vibrating tools
      • Commonly seen in manual workers, dentists, road workers
      • Causes hand-arm vibration syndrome
        • = a secondary form of Raynaud syndrome
    • Whole body vibration
      • Due to riding machinery, etc.
      • Causes fatigue, irritability, disorders of the spine, etc.
    • Prevention
      • Use tools which vibrate less
      • Avoid cold
      • Anti-vibration gloves
      • Spend less time vibrating