protective eyewear Flashcards
what are we protecting our patients against?
- penetrating trauma
- chemical burns ( alkali or acidic )
what is impact resistance?
the ability of a material to withstand a high force or shock applied to it over a short period of time
how are materials tested?
- materials are tested with the drop ball test and graded in terms of impact resistance
what is the affect of elasticity?
- the elasticity of material is what give the material its impact resistance
- elastic material is able to absorb some of the shock/force that hits it and lens doesn’t break
how should the frame and lens be ?
- the frame needs to be loose enough that if the lens is flexing during this period of elasticity that its got somewhere to go
- lens isn’t glazed too tight
what are some health and safety regulations?
- BS EN 166:2002 personal eye protection : specifications
- BS EN 167:2002 personal eye protection: optical test methods
- some regulations for sport
what is CE mark ?
shows that product is meeting all European standard for health and safety
what are types of protective eyewear ?
- spectacles that are glazed with prescription
- some can be worn on top of spectacles ( temporary measure )
- googles ( protect around ocular area ) - can also be ventilated
- visors - protect the whole head
A screw comes out of the side of a PX safety glasses that he uses for work and asks to put a new one in - what do you say?
no, as this will void the manufacturer guarantee
- you need to send back to manufacturer who will re-test the unit and ensure that its meeting standards
what are lens marking?
lens markings show that if a lens has met standards but only found if applicable
what are examples of lens markings?
. scale number ( filter lenses ) . manufacturers mark - always relevant . optical class . mechanical strength symbols . field of use . scratch resistance . resistance to fogging . radiant heat
what are some examples of frame markings?
. frame should always be marked - this is because frame also has standards
- manufactures mark
- appropriate European standard number EN166
- field of use - intended use
- mechanical strength
- CE mark
what is protective eyewear considered as ?
considered as a single unit- must be tested as such
what are scale numbers?
- higher numbers= darker filters
- consists of code number and a shade number
what is optical class
- 1,2 or 3 - indicates the optical quality of the ocular
- how close the prescription is what is should be
1= in tolerance with what the prescription is expected to be . +/- 0.66 D - as numbers get bigger tolerance is lower
what is mechanical strength ?
- looks at impact resistance
e. g bearing test - can be marked with various codes
- most safety spectacles are marked with an S or F
- S= increased robustness
e. g. CR39- not very tough - F= low energy impact
e. g. polycarbonate - B= medium energy impact
e. g. goggles - A = high energy impact
e. g visors or face shield or some goggles
what is field of use?
- what spectacles are going to be used foe
. resistance to surface damage . resistance to fogging . liquid droplets/ splashes . large dust particles . circuit electric arc . gas/fine dust particle . molten metal/ hot solids
what does filed of use depend on ?
- occupation
- work place assessment - what risks are in the work
what should safety lenses have ?
safety lenses must be resistant to impact - requires a certain centre thickness to allow an impacting particle to be deflected
- type of thickness depends on material and what is being used for and how its being made tough
what materials make a good safety lens material?
polycarbonate-
trivex-
glass - must be treated to meet S standard
what are the pros and cons of using plastic lenses as protective eyewear?
- more elastic than crown glass
- impact resistance depend on material
- impact resistance is affected by coating
- CR39 can break intro hooked shards
what are pros and cons of using glass as protective eyewear?
- untreated is not suitable for protective lenses
- can be heat or chemically toughened
- laminated
what are pros and cons of using trivex as protective eyewear?
- higher v value compared to polycarbonate
- UV cut off to 400nm
- tinting not possible
- good chemical resistance
- n=1.54
- ## lowest specific gravity
what is a compression envelope ?
- outside of the lens is put into compression - molecules at the lens surface closer together compared to the centre
- allows lens to become stronger
- heat and chemical toughening both produce compression envelopes
what does force cause in an untreated glass?
untreated glass- force causes compression at blow and release tension on the other side
what does compression result in a treated glass?
- compression results in point opposite impact remaining in compression
- treated glass remains okay
what does damage to surface do to compression?
damage to surface reduces compression
what are the two main methods of toughening a glass lens ?
- heat toughened
- chemically toughened
how is heat toughening carried out?
- lenses must be glazed before toughening
- requires a minimum centre/edge thickness of 2.4 mm
- lens is heated just below melting point 650 c
- thicker lens= heated longer
- variable heating time
- outer glass cools more rapidly than centre
- if it does smash then blunt pieces
- rejection rate compared to chemically toughened
- can be recognised by Maltese cross on a polarising filter
how is chemical toughening carried out?
- lenses must be glazed before toughening
- lenses placed in 440c molten potassium nitrate bath for 16hrs
- ion exchange occurs between 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
what is compression envelope caused by ?
- caused in difference in cooling between the surface and centre
what should you remember when supplying protective eyewear?
- if protective eyewear is supplied as industrial prescription protective eyewear then the employer is required to assess the workplace risk
- you need ti supply to the company order form
- if you do perform a workplace assessment you must keep detailed case records of the assessment
