LAW; u r getting there. Flashcards
what are the types of eye protectors?
- spectacles with or without side shields
- moulded eye shields
- box type googles
- cup type googles
- welding helmets
- face shields
- hand held welding shields
- face masks
what are the characteristics of safety spectacles?
- not suitable for dust, gases, molten metal, hot solids, liquid droplets or splashes (BS EN 166)
- can be made to fit well
- available in plastic frames-safer than metal
- available in metal frames:
- –more damage when impacting on face
- –pads cause injury to the nose
- –screws work loose
characteristics of safety spectacles with side shields?
- must be transparent and not discolour
- injection moulded are best, as they do not wrap to leave gaps
- polycarbonate material ideal
- may be perforated for ventilation
characteristics of moulded eye shields (afocal one-piece, wrap around)?
- moulded from single piece of polycarbonate
- great for emmetropes
- usually only one size
- often supplied by employer-but lack of fitting.
- employees’ typical complaints:
- –restricted field of view
- –slight magnification effect
- –reflections
- –peripheral displacement effect
characteristics of googles-cup type?
- housing made from PVC and tight fit
- good for flying particles such as metal,dust, etc
- suitable for welders
- adjustable nasal fitting
- screw rim to allow for glazing
- large bridge aprons to protect the nose are available
- disadvantages:
- –cannot be worn over spectacles
- –poor ventilation
- –uncomfortable
- –poor peripheral vision
characteristics of box-type googles?
- normally made of PVC, good fit
- one piece lens: polycarb/cellulose acetate or possible toughened glass
- can be worn over spectacles
- well ventilated, lightweight
- wide field of view
disadvantages:
- –nasal fitting not adjustable
- –replacing one-piece lens
characteristics of face shields?
- good for protection against splashes and flying particles
- headband-supported vision that cover the face and neck
- easily worn over specatacles
- excellent FOV
- polycarbonate/ cellulose acetate
- can be handles for welding screens
- motorbike helmet, security guards etc!
characteristics of helmets,
- mostly for welding
- protection against intense heat and splatter
- contains filter for radiation protection
- most have a cell which darkens to welding density as soon as the arc is struck
- sometimes have own air supply as gases from welding rods are toxic
what are the lens materials for eye protectors?
- Glass
- heat-thoughened
- chemically-thoughened
- laminated - Plastic
- PMMA (perspex)
- CR39
- Polycarbonate
- Trivex
- Cellulose Acetate
What are the characteristics of heat-toughened glass?
- crown lens placed in furnace at 637’c for 50-300s
- lens cooled rapidly (cold air)
- sudden cooling creates compression at surface and tension within lens mass- ‘compression envelope’
- quick and cheap process
DISADVANTAGES:
- high plus powers require prolonged heating
- lenses will be thicker
- scratches reduce impact resistance
- photochromic lenses do not work well if toughened
- strain tester pattern (maltese cross)
characteristics of chemically toughened glass?
- more popular in US
- compression coat formed by chemical process
- preheat lens and immerse in KNO3 at 470’c for 16hours
- large K+ ions exchanged for smaller Na+ ions in glass- 100microm compression coat applied
- thinner than heat-toughened but greater impact resistance
- all lenses take the same time to toughen
- no warping
- expensive process
- hard to tell when material has been toughened
What are the results in breakage of toughened glass?
- radial fracture pattern
- sometimes concentric cracks
- only a few splinters formed
- fragments tend to stay in the frame
what are the characteristics of laminated glass?
- two layers of crown glass with inner layer of plastic material
- impact resistance only slightly higher than crown glass
- supposed to stick to plastic if it shatters-not always
- silvers from back may come off into eye
characteristics of plastic materials?
- greater impact resistance
- fragments tend to be large and blunt
- 50% weight cf glass
- some powers will be thinner in glass, as no need to thicken for impact resistance
- withstands molten metal and hot sparks better, as metal does not fuse with surface
- less condensation (lower thermal conductivity)
- greater Uv protection than glass
disadvantages:
- easily scratched
- hardcoat reduces impact resistance
why do we need eye protectors?
to defend against:
- molten metals and hot solids
- gases
- dust
- impact of different severities
- optical radiations
- droplets and splashes
characteristics of PMMA & CR39?
- PMMA = ICI perspex and now largely replaced by CR39
- CR39 greater impact resistance, but sharper fragments.
- both suitable for eye protectors
- CR39 can be tinted unlike PMMA
characteristics of polycarbonate?
- high impact resistance
- very soft
- quartz coating often used but can reduce impact resistance from 224ms to 152ms
- good for children’s spex
- cracks on impact
- no warping or chipping
- very lightweight
- refractive index: 1.586
- absorbs UV
- accompanied by colour fringes in periphery
what are the characteristics of trivex?
- highest impact resistance (low energy impact grade)
- unaffected by most common chemicals and solvents
- lightweight and thin
- V value: 45 (reduced chromatic aberration)
- refractive index: 1.53
- high tensil strength make it resistance to cracking
- 100% protection against UV
- good for children’s spex
what are the characteristics of cellulose acetate?
- only used for basic eye protectors due to relatively poor impact resistance
- good resistance to chemicals
How to test the resistance?
- impact resistance
- influenced by
- ->scratches on lens
- ->size and speed of missile
- ->lens thickness
- ->lens material
* CR39 more impact resistance than glass
* heat more impact resistance than chemically toughened glass
* impact resistance improves with lens thickness and curvature - surface hardness
- a thinly coated (5microm) polycarbonate lens is superior to an uncoated CR39 lens - chemical resistance
- glass lens resistant to most chemicals
- plastics can craze but CR39 has relatively good resistance - thermostability
- polycarb & PMMA are prone to distort more radily than glass - resistance to hot particles
- glass easily pitted as hot particles fuse with glass material
- plastics do not pit easily due to elasticity of surface when heated. - radiosensitivity:
- if particles penetrate the eye it is helpful if they are visisble on x-ray
- glass can be seen if > 0.5mm
- plastics very hard to fine - flammability
STANDARDS AND REGULATIONS:
- CE mark
- most PPE must be certified with 3. things: independent insoection, basic safety requirements, CE marked
- illegal for suppliers to sell PPE without the CE mark - includes all spectacle frames - British Standard (BS)
- health and safety executive (HSE) publish guidance on PPE regulations
- these refer to BS and european standards
- most relevant to optometrist is BSE EN166 personal e ye protection-specifications
what are the two things that an optometrist must do after get qualified?
- Get professional indemnity insurance
2. Register with GOC (General Optical Council)
what is professional indemnity insurance?
- One must hold professional indemnity insurance cover valid for UK purposes in order to register with GOC
- one must not carry out any professional work outside the terms of the insurance policy
- The cover must be in place before the GOC accept the application for registration
How to get professional indemnity insurance?
- join a professional body that provides it
- Association of Optometrist (AOP)
- Federation of Opticians (FODO) - check if covered by employer
- note well that if take this insurance, one wont be covered for any other professional activity elsewhere (locum)
- most optometrist have their own AOP or FODO cover - Buy a policy on the open market