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Dispensing Viva > Protective Eyewear > Flashcards

Protective Eyewear Flashcards

1
Q

Hazards

A

Penetration trauma and chemical burns

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2
Q

Impact Resistance

A

= the ability of a material to withstand a high force or shock applied to it over a short period of time

  • materials are tested with the drop ball test and graded in terms of impact resistance
  • affected by the elasticity of the material
  • greatly affects the safety of the lens
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3
Q

Elasticity and Frame

A
  • if a material is quite elastic, it can absorb some of the shock/force that hits it. If its a brittle material it may crack
  • frame needs to be loose enough that if lens is flexing during this period of elasticity, it has somewhere to go
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4
Q

Types of Eyewear

A
  • spectacles worn over glasses - should be seen as a short term measure
  • goggles - protect around ocular area against gases etc
  • visors/face shields - protects whole head
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5
Q

Personal Protective eyewear and adjustments

A
  • can make small adjustments but cant repair or replace any parts.
  • have to send it back to the manufacturer who will repair and retest the unit to make sure its up to standard
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6
Q

Lens Markings

A 
1- scale number (filter lenses) eg uv
2- manufacturers mark 
3- optical class 
4- mechanical strength symbols 
5- field of use 
6- scratch resistance 
7- resistance to fogging 
8- radiant heat 
markings are listed in this order and lenses are only marked with markings that are applicable
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7
Q

Frame Markings

A 
1- manufacturers mark 
2- appropriate european standard number EN166
3- field of use 
4- mechanical strength 
5-CE mark
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8
Q

1) Scale Numbers (LM)

A
  • higher numbers = darker filters

- consists of a code no and a shade no

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9
Q

3) Optical Cross (LM)

A
  • 1,2,3 - indicates optical quality
  • indicates how close rx is to what it should be
  • 1 is the best, v close to tolerance
  • as no gets bigger, tolerance decreases
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10
Q

4)Mechanical strength

A

S= increased robustness
F=less energy impact
B=medium energy impact ie goggles
A= high energy impact ie visors and goggles

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11
Q

5) Fields of use

A

Depends on occupation and workplace assessment

  • resistance to surface image
  • resistance to fogging
  • liquid droplets/splashes
  • large dust particles
  • gas/fine dust particles
  • molten metal/ hot solids
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12
Q

Safety lenses

A
  • lenses must be resistant to impact - requires a certain centre thickness to allow an impacting particle to be deflected
  • good examples are polycarbonate and trivex
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13
Q

Plastic Lenses

A
  • more elastic than crown glass
  • impact resistance depends on the material
  • impact resistance is affected by coatings
  • CR39 can break into hooked shards
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14
Q

Polycarbonate Lenses

A
  • good for safety lens material generally
  • good for impact resistance
  • not good for chemical resistance - if used with acetone, lens goes milky
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15
Q

Trivex

A
  • higher v value compared to polycarbonate
  • uv cut off to 400nm
  • tinting not possible
  • good chem resistance
  • n=1.53
  • lowest specific gravity of any lens
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16
Q

Glass lens

A

-untreated isnt suitable for protective lenses - material can be heat/chemically toughened or laminated

17
Q

Compressed envelopes

A
  • heat and chem toughened both produce compression envelopes
    -outside of the lens is put into compression - molecules at the lens surface closer together compared to the centre
    untreated glass = force causes compression at blow and release of tension (fracture) on the other side
    treated glass = compression results in point off impact remaining in compression
  • damage to surface reduces compression
18
Q

Heat toughened

A
  • lenses must be glazed before toughening
  • requires a minimum centre/edge thickness 2.4mm
  • lens is heated to just below melting point 650 degrees
  • variable heating time
  • outer glass cools more rapidly than centre
  • if it does smash, then blunt pieces
  • rejection rate
  • can be recognised by maltese cross on a polarising filter
19
Q

Chemically toughened

A
  • lenses must be glazed before toughening
  • lenses placed in 440 degrees molten potassium nitrate bath for 16hrs
  • ion exchange occurs bet potassium ions in the bath and smaller sodium ions at the lens surface
  • thin and uniform compression envelope created. No minimum lens thickness required - greater impact resistance when compared to heat toughened
  • no identification possible
  • expensive equipment required
20
Q

Industrial protection protective eyewear

A

when supplied, the employer is required to assess the workplace risk

  • you may need to supply to the company order form
  • if you do make perform a workplace assessment you must keep detailed case records of the assessment

Dispensing Viva (12 decks)

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