L11 Protective eyewear Flashcards
1
Q
Hazards
A
Penetration trauma and chemical burns
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
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
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
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
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
7
Q
Frame Markings
A
1- manufacturers mark 2- appropriate european standard number EN166 3- field of use 4- mechanical strength 5-CE mark
8
Q
1) Scale Numbers (LM)
A
- higher numbers = darker filters
- consists of a code no and a shade no
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
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
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
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
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
14
Q
Glass lens
A
-untreated isnt suitable for protective lenses - material can be heat/chemically toughened or laminated
15
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
