Radiation B7 Atom Radiation • Two main types: – Ionising – Non- inonising Ionisation Types of ionising radiation • Particulate radiation • Electromagnetic ALPHA PARTICLES • Stable groups of two protons and two neutrons • Comparatively large, travel short distances in dense materials, and are unlikely to penetrate living skin tissue, as the dead layer of skin at the surface of the epidermis will prevent entry. • The principal risk is through ingestion or inhalation of a source of alpha particles, which might place the material close to vulnerable tissue. BETA PARTICLES • Beta particles (β-) are electrons, which are negatively charged particles. • Much faster moving than alpha particles. • Smaller in mass than alpha particles, but have longer range, so they can pass through several metres of air and penetrate the skin. • Less ionising and take longer to affect the same degree of damage. GAMMA RAYS • Gamma rays (λ.) are photons of electromagnetic radiation that are emitted by the nucleus of an unstable atom. • Gamma rays are 'packets' of electromagnetic energy that possess a characteristic wavelength similar to, but shorter than, Xrays. • They have great penetrating power. X-RAYS • X-rays are photons of electromagnetic radiation that are either produced artificially or occur as part of radioactive decay, when atoms re-arrange themselves to release energy and become more stable. • X-rays have high energy, and high penetration power through fairly dense material. In lowdensity substances, including air, they may travel long distances. NEUTRONS • Neutrons (n or n0) are single particles emitted during certain nuclear processes, for example, nuclear fission. • Great penetrating power and are able to pass through relatively dense materials such as 50 mm of lead. PARTICULATE IONISING RADIATION • When radioactive material transforms by decay, it can emit 'beta particles' (electrons), 'alpha particles' (two protons and two neutrons) and/or single neutrons. • The radionuclide uranium-238, found in all rocks, soil, and the food we eat, emits (predominantly) alpha particles. Activity • The amount of radiation produced by radioactive material is governed by the number of disintegrations occurring per second and is called activity. • The SI unit of activity is the Becquerel (Bq). 1 Bq equals 1 disintegration per second Half-life • The speed with which atoms radioactively decay varies from one substance to another and is characterised by radioactive decay at a fixed rate called the half-life. NON –IONISING RADIATION • Non-ionising radiation relates to the part of the electromagnetic spectrum covering two main regions, optical radiation (ultraviolet, visible and infrared) and electromagnetic fields (power frequencies, microwaves, and radio frequencies). Electromagnetic Spectrum ULTRAVIOLET RADIATION • Ultraviolet (UV) radiation is emitted from very hot bodies, for example, electric arcs and the sun. Possible occupational sources • • • • • • • • The sun. Electric arc welding and cutting. Sun beds and sunlamps. Crack detection equipment. Water treatment. Adhesive curing equipment. Mercury vapour lamps. Tungsten halogen lamps. Ill-Health effects due to exposure to UV light • Excessive exposure leads to: • Photokeratitis (inflammation of the cornea). • Photoconjuctivitis (inflammation of the conjunctiva). • The induction or promotion of cataracts (the lens of the eye becomes opaque). • Damage due to an acceleration of the normal ageing of cells in the retina. EXPOSURE TO ULTRAVIOLET RADIATION (8 h period) • Exposure of the eyes – Ultraviolet radiant exposure in the spectral region: – 180 to 400 nm incident upon the unprotected eye(s) should not exceed 30 J m-2 – 315 to 400 nm should not exceed 104 J m-2. • Exposure of the skin – For the most sensitive skin phototypes (known as 'melanoma-compromised'), ultraviolet radiant exposure in the spectral region of 180 to 400 nm should not exceed 30 J m-2. UV Light meter UV TANNING EQUIPMENT A leisure spa is planning to install UV tanning equipment. The equipment uses UV sources with a higher intensity than normal sunlight in order to accelerate tanning. Outline control measures that should be put in place for BOTH employees AND customers for the safe operation of this facility. (16) PRECAUTIONS TO BE TAKEN WHEN USING UV TANNING EQUIPMENT • • • • • • • • HEALTH SCREENING PROVISION OF INFORMATION TO USER SKIN CREAMS & EYE PROTECTION REGULAR CLEANING OF EQUIPMENT REDUCE EXPOSURE – TIMERS SUPERVISION BY COMPETENT PERSONS REGULAR MAINTENANCE OF EQUIPMENT INTERLOCK SYSTEMS FOR MAINTENANCE WORKS METAL ARC WELDING • Outline the precautions to be taken for workers carrying out metal arc welding. Hazard classification of lasers (BS EN 60825-1:2014) Class Class 1 Characteristics Inherently safe laser products. Safety is achieved either due to their low power or by their total enclosure, for example, laser printers, CD players. Class 1M Either a highly divergent beam or a large diameter beam, therefore only a small part can enter the eye. Harmful if viewed through magnifiers, for example, fibre optic communication systems. Class 2 Maximum output of 1 milliwatt (mW), wavelength between 400 and 700 nm. Damage to the eye is prevented by blinking and averting the head, an instinctive response. Repeated deliberate exposure is not safe, for example, laser pointers and barcode scanners. Class 2M Either a highly divergent beam or a large diameter beam, therefore only a small part can enter the eye, limited to 1 mW. Harmful if viewed through magnifiers or for long periods, for example, civil engineering applications - level and orientation instruments. Class 3R Higher powered than classes 1 and 2. Max output of 5mW, exceeds max permissible exposure for accidental viewing and can cause eye injuries, but the actual risk of injury following a short exposure is small. This class replaces the former 3A and lower part of 38, for example, some laser pointers and some alignment products for home improvement work. Class 3B Output power of 500 mW (half a watt). Causes eye damage from direct beam exposure and reflections. Extent of injury depends on radiant power entering eye and duration of exposure, for example, lasers for physiotherapy treatment and research lasers. Class 4 Output greater than 500 mW, with no upper restriction. Causes injury to eye and skin and a fire hazard for example, lasers in displays, laser surgery and cutting metals. CAOR 2010 • The Control of Artificial Optical Radiation at Work Regulations (CAOR) 2010 specifies that the employer must put in place actions to limit exposure to artificial optical radiation so that the exposure limit values (ELVs) are not exceeded. • Risk Assessment • Laser Safety Officer • (a) Identify the hazard classification system for lasers. (2) • (b) Low power lasers are widely used to read bar-code labeled products at checkouts in retail premises. • Outline: – (i) the design features; (4) – (ii) the procedural controls (4) – that should be in place for the safe operation and maintenance of this equipment.
