Eye Protection & British Standards 1 Flashcards
Describe mechanical hazards to eye?
- Mechanical impact can cause damage to, or loss of, an eye by irritation, contusion, penetration, or crushing
- Permanent effects include conditions e.g. corneal scarring, traumatic cataract and lens dislocation.
- Problems can arise from:
o Dust, fast moving small particles or chips from filing, drilling, or hammering, which will irritate and damage the cornea, conjunctiva, sclera or lids.
o Larger particles, from fragments of broken material to squash balls which cause contusion or crushing to the eyeball.
o Splashes of molten metal which cause damage due to their mechanical force and due to their temperature.
o Falls and explosions
Describe chemical hazards to the eye?
- Damage to external parts of lids, cornea, conjunctiva and lachrymal apparatus.
o Some of these are very serious as they cause permanent visual damage or loss – e.g. corneal scarring. - Harmful chemical damage is caused by acid from batteries, alkalis (cleaning fluids), bleaches in dye works (chlorine, hydrogen peroxide), and a wide range of organic solvents (turpentine, carbon tetrachloride, acetone).
- Alkalis are particularly harmful because they progressively dissolve the material of the cornea, instead of forming some sort of precipitate that slows down the action of the chemical.
- Even low concentrations of gas or from dust particles can cause external irritation in workplace atmosphere.
o Since such problems tend to be cumulative they get worse as day/week goes on.
o CLs, which tend to accumulate the contaminant, can be a particular problem. - Chemical poisons may reach visual pathways indirectly though ingestion or absorption through the skin.
o May cause toxic amblyopia, with concomitant visual field and colour vision effects.
o These problems tend to be permanent and require a prolonged exposure to the hazard
Describe other hazards to eye?
- Atomic radiation - ionising radiation can cause radiation cataract. In v high doses retinal haemorrhaging may occur.
- Electrical injuries - caused by lightning or manmade devices cause lesions in both to outer & inner eye.
o Most common effect is electrical cataract, forming sometime after accident. - Ultrasonic injuries - from powerful ultrasound sources used in diagnostic techniques (e.g. ultrasonography of foetuses).
o Incorrect use can cause lenticular opacities and chorio-retinal lesions
Need to be trained to use them - Hyperthermal injuries - causing flame burns or contact burns from hot solids/liquids in the eye.
- Stress injuries - from rapid decompression (divers), excess vibration or acceleration (military aircrew) give a temporary inflammation of or bruising to ocular structures.
- These injuries are getting less and less obvious in the workplace as the Health and Safety Standards are improved periodically
How can you contain hazards at source?
- Using screens or guards around machines or processes to ↓radiation hazards (opaque screens) & impact resistant transparent screens that allow work to be seen but reduce mechanical and chemical hazards.
- Modifying transfer process of chemically hazardous substances using enclosed pipes, or by using a stream of lubricant around lathes to ensure that mechanical hazards such as flying particles to do not injure the workforce.
- Changing material that constitutes the hazard, e.g. replacing ordinary glass for laminated glass in car windscreens.
- Training workforce to recognise the risks & ensuring that there exist good lighting and safety practices, such as keeping the area free of obstacles
Name the British Standard on eye protection?
- British Standard on eye protection is BS EN 166 (1996) Personal eye protection - specifications.
- Eye protector: Any form of eye protective equipment covering at least region of the eyes
What is the function of eye protectors?
- The function of eye protectors is to provide protection against:
o Optical radiations (wavelength 0.1m to 1000m)
o Molten metals and hot solids
o Droplets and splashes
o Dust; Gases
o Short-circuit electric arc or any combination of these
Describe spectacles as eye protector/
o Eye-protector with oculars mounted in a spectacle-type frame, with or without side shields.
o Conventional safety glasses with robust frames, impact resistant lenses and side-shields offer modest protection against mechanical hazards.
o Offer some protection against chemical hazards and radiation hazards (if suitably tinted).
o Spectacles are not suitable for protection against medium- and high-energy impact, dust, gases, molten metal, hot solids, liquid droplets or splashes
Describe one piece eye protectors?
o Usually moulded from polycarbonate
o Useful for emmetropes because there are no lenses to be dislodged from the frames. They may not be so suitable if a refractive correction is required
Describe cup type eye protectors?
o Individual eyepieces connected with a flexible bridge of some sort.
o Advantages:
Excellent eye enclosure; lenses easily changed; adjustable bridge; nose protection possible.
o Disadvantages:
Bridge adjustment may not go small enough; poor ventilation which causes the lens to mist; uncomfortable; field of view restricted.
o They are used in welding and grinding work, small high-velocity particle hazard
Describe goggles eye protectors?
o Eye-protector that tightly encloses orbital area and sits on the face.
o Goggles are available in two forms:
o Box type - a single moulding covers both eyes and the bridge of the nose.
o Advantages:
full central field of view; wide field of view; one piece lens; good fitting with PVC surround; good ventilation; worn over specs; grade 1 impact, dust, gas, chemical and molten metal protection.
o Disadvantages:
no adjustment of nasal fitting; limited ability to tint or change lens; easily scratched; difficult with multifocals; may impact on spectacles underneath.
o They are used in heavy and hazardous industrial processes
Describe face shield eye protectors?
o Eye-protector covering all or a substantial part of the face.
o Normally a suitable headband, helmet, protective hood or other appropriate mounting devices are incorporated into face shields
o Advantages:
Whole face protection; worn over spectacles; full field of view; protection to impact grade 1; protection against chemical splashes possible; gas welding protection possible with tint.
o Disadvantages:
easily scratched; heavy.
o Examples: motorcycling, cricket. Any process where whole face is at risk from large, high velocity particles
Describe welding hand-shield eye protectors?
Hand-held device protecting eyes face & neck
Describe welding helmet eye protectors?
o Device worn on the head, protecting eyes, face, neck, & all or part of the top of the head.
o Face masks with a glazed aperture are standard in many types of welding.
o Opaque material of the mask is proof against mechanical, chemical and radiation hazards.
o The glazed filter can be changed to provide protection for both electrical and gas welding, which require different types of filters, due to the different types of radiant energy produced by the two processes
Describe thermally toughened glass as materials for eye protectors?
o Lens is heated to about 600OC for a few minutes. Thereafter it is cooled rapidly which creates a compression tension coat referred to as the compression envelope. This improves the impact resistance.
o Advantages:
Heat-toughening is a relatively quick and cheap process.
o Disadvantages:
Rx lenses > +5 D require prolonged heating. This may cause warping which degrades the optical properties.
Rx lenses > -5 D have poor impact resistance due to relatively small centre substance.
A heat-toughened lens is always thicker than untoughened lens of equivalent power.
Heat-toughened lenses do not retain the same level of impact resistance throughout life due to scratches and other surface abrasions.
Heat-toughening process reduces the range of the original transmission of photochromic lenses.
Heat-toughening process induces shadow or strain patterns
Describe Chemically toughened glass as materials for eye protectors?
o A compression-tension coat is produced by a chemical process. This technique includes preheating and treating by a potassium nitrate solution at 470OC for 16 hours. The smaller sodium ions present in the glass are exchanged by the larger potassium ions present in the solution. This produces a very thin (100 m) and tough compression coat and does not affect the photochromic activity of lenses.
o Advantages:
Chemically toughened lenses are thinner than heat-toughened lenses.
They have greater impact resistance as compared to heat-toughened lenses.
Chemically-toughening is suitable for lenses of wide range of thickness.
This technique uses lower temperature than that used for heat toughening which results in absence of warping.
o Disadvantages:
Chemically toughing process requires expensive equipment.
It requires more expensive glass for the best result.
Rx lenses > +5 D require prolonged heating – may cause warping which degrades optical properties.
The thin compression coat is damaged by scratches reduces impact resistance.
Conventional methods cannot determine whether the lens has been toughened employer won’t know just by looking at it
