Comprehensive details of required illuminance values in given locations are provided in CIBSE Code for Lighting. Further information BS EN 12464 \200\2231 (2011). Light and lighting \200\224lighting of wo rk places. Part 1: indoor work places. Available at: M http://shop.bsigroup.com/ BS EN 12464 \200\2232 (2007). Light and lighting \200\224lighting of work places. Part 1: o utdoor work places. Available at: M http://shop.bsigroup.com/ BS 5266 \200\2231 (2005). Emergency lighting regulations. Available at: M http://shop.bsigr oup.com/ CIBSE (2009). Code for Lighting . CISE. London. Available at: M http://www.cibse.o rg/ Health and Safety (Display Screen Equipment) Regulations (1992). Available at: M http:/ /www.hse. gov.uk/pubns/priced/l26.pdf HSE (2002). Lighting at work , HSG38. HSE Books, Sudbury. Available at: M http://www.hse.go v.uk/ pubns/books/hsg38.htm Smith NA (2000). Lighting for Health and Safety . Butterworth-Heinemann, Oxford. 01_Smedley_Chap01.indd 15 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 16 Ionizing radiation 1: Types, units, and effects Routes and sources of exposure \200 The h azard from ionizing radiation can arise from: the uniform irradiation of the whole body or part of the body (external radiation) irradiation due to inhaled or absorbed radioactive material, which may concentrate in organs and tissues (internal radiation). \200 Natural (background) rad iation arises from several sources, including radiation from materials in the earth \200 \231s crust (e.g. radon in granite strata), cosmic radiation, food, radioactive aerosols, a nd gasses in the atmosphere. The largest dose of radiation, approximately 85% of the total, received by a person living in the UK is due to natural background radiation. Typically, t his can amount to 2.2mSv per year (see b p. 16, Units of ionizing radiation). Sources of ionizing radiation \200 Sealed : contained or shielded, and present only an ex ternal radiation hazard Unsealed : can be released into the atmosphere because they: are powders, liquids or gasses; \200 can contaminate surfaces and be taken into the body by ingestion, inhalation or via the skin, thereby giving rise to an internal radiation hazard, which can be present for variable periods of time. Types of ionizing radiation \200 Alpha particles: these are positively charged particles consisting of two protons and two neutrons (the same as a helium atom nucleus) with relativ ely little energy (they cannot pass through a sheet of paper or intact skin), but capable o f causing signi \201 cant damage to tissue over a short range. Beta particles: these are electrons and are also charged (negatively). They are much lighter than alpha particles and can pass through paper and skin, although th ey can be stopped by materials such as glass or thin layers of metal. Neutrons: these are uncharged particles with intermediate mass and variable energy. Gamma and X-rays: these are uncharged and without mass. They therefore cause less damage to tissue, but can pass through many materials, although are attenuated by thick layers of le ad or concrete. Units of ionizing radiation Activity This indicates the rate of transformations in radioact ive material. The unit is the becquerel (Bq). 1 Bq = 1 transformation/s 01_Smedley_Chap01.indd 16 12/31/2012 8:42:05 PM IONIZING RADIATION 1: TYPES, UNITS, AND EFFECTS 17 Absorbed dose This is the measure of energy deposition in any irradiated material by all ty pes of ionizing radiation, and is expressed as the energy absorbed per unit mass of materia l. The unit of absorbed dose is the gray (Gy): 1Gy = 1J/kg of energy deposition. Dose equivalent In biological systems, the same absorbed dose of different types of radia- tion produces different degrees of biological damage. To take account of this, the absorbed dose of each type of radiation is multiplied by a Q (or weighting) factor, which re \202 ects the relative ability of the particular type of radiation to cause damage. The unit of dose equivalent is the sievert (Sv), which is related to the gray as follows: dose equivalent (Sv) = absorbed dose (Gy) \227 Q. (Occupational doses of radiation are quoted in millisieverts (mSv) in view of the levels of radiation received.) For beta particles, gamma and X-rays, Q = 1. For (cid:2) particles, Q = 20. For neutrons, on average, Q = 10. Effective dose Similarly, the risk to various tissues varies from one tissue to another; it is not the same for any given equivalent dose. There is thus a weighting fac- tor for each tissue, when multiplied by the equivalent dose, the sum of all such calculations for the v arious tissues is referred to as the effective dose and is a single measure of the risk of detriment to health. Health effects \200 Damage to tissue sustained by an irradiated indi vidual is termed \200\230somatic \200\231 effects . These can be acute or delayed. That passed on to descen dants is the hereditary effect. Stochastic effects are those for which risk (the probability of the effect) increases progr essively with dose received, but there is no detectable threshold (e.g. induction of carcin ogenesis). The risk of developing cancer for radiation workers is calculated as 4% per Sv. Deterministic effects are those for which the severity of the effect increases progressively with dose and will not occur until a certain threshold of dose has been received (e.g. radiation burn). 01_Smedley_Chap01.indd 17 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 18 Ionizing radiation 2: Principles of radiation protection Justi \201 cation The use of sour ces of ionizing radiation or radioactive materials must be justi \201 ed in terms of risk and bene \201 t. Optimization Work with sources of ionizing radiation must be such as to r educe risks to levels that are as low as reasonably achievable (in practice, \200\230achie vable \200\231 becomes \200\230practicable \200\231). Dose limits \200 Dose limits are r ecommended by the International Commission on Radiation Protection (ICRP), with the aim of preventing non-stochastic (deterministic) effe cts and limiting stochastic effects. \200 Current dose limits for UK workers and the publ ic are published in the Ionizing Radiations Regulations 1999 and are shown in Table 1.2. Table 1.2 UK annual dose limits (mSv) Annual dose limits Whole body Skin Lens of the eye Radiation workers (classi \201 ed) Trainee (under 18) Radiation workers (non classi \201 ed) Others, including members of the public 20 6 6 1 500 150 50 50 150 50 15 15 The dose limit to the abdomen of a woman of reproductive capacity is 13mSv in any consecuti ve 13-wk period. The dose limit to the fetus once pregnancy has been declared is 1mSv durin g the period of the pregnancy. From HMSO (1999). Ionizing Radiations Regulations . HMSO, Lo ndon. Available at: M http://www.hse.gov.uk/pubns/books/l121.htm 01_Smedley_Chap01.indd 18 12/31/2012 8:42:05 PM This page intentionally left blank CHAPTER 1 Physical hazards 20 Ionizing radiation 3: Instrumentation and measurement Environmental radiation detectors A w ide range of instruments are available. Instruments are based on several types of detectors (gas ionization, solid state detectors, change in chemical systems, and neutron activation ) and are used to quantify incident radiation as a count or dose rate. Such detectors inclu de: \200 Installed ( \201 xed) monitors: used to monitor personal contamination, general radiation, and air contamination level in the working environment Portable (battery operated) monitors: used to measure levels during speci \201 c operations and for contamination surveys. Devices for personal monitoring Movie badges \200 Movie is developed and analyzed for ext ernal radiation dose, in proportion to darkening of the \201 lm Various \201 lters inside the badge differentiate types of radiation and energies Developed \201 lm can be stored to provide a permanent record, which can be read again at a later date They are no longer widely used as they are less practical and more expensive than TLDs. Thermoluminescent dosemeters (TLDs) \200 Can measure over a wide range for both whole bod y and extremity ( \201 nger) monitoring Popular dosemeter for personal monitoring, as they are small and analysis can be performed quickly and automatically Not as sensitive to the effects of heat and humidity as \201 lm badges \200 They are mo re sensitive to low doses than \201 lm badges \200 Dose information is destroyed at rea dout, unlike \201 lm badges. Direct reading instruments \200 Use for direct measurement of X-rays or gamma rays \200 Self-indicating pocket dosemeters (similar in size to a fou ntain pen or a radio-pager) are useful for measuring doses in situations where the dose rat e is high, allowing a continuous watch to be kept on the rate of accumulation of dose Must be calibrated with known dose levels \200 Can lose sensitivity with leakage, and ten d to be insensitive to low levels of radiation. 01_Smedley_Chap01.indd 20 12/31/2012 8:42:05 PM IONIZING RADIATION 3: INSTRUMENTATION AND MEASUREMENT 21 Unsealed radiation sources \200 Surface contamination: monitoring in the work area and on the worker \200\231s skin, and clothing is detected by portable and \201 xed monitors, includ ing before workers leave a controlled area Airborne sampling: as with dusts, certain types of radioactive material can be sampled on \201 lter paper using a high volume sampler. Particulate or gaseous act ivity is then measured by scanning the \201 lter for radioactivity using a counter. Radio active gasses can also be collected using a sampling bag or chamber Biological monitoring: total internal dose is determined in special cases by measuring urin e or stool samples. Biological effect monitoring can be done by examining lymphocyte chromo somes from a blood sample. 01_Smedley_Chap01.indd 21 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 22 Ionizing radiation 4: Exposure control General requirements \200 Demarcating speci \201 c areas and classi \201 cation of personnel based on their radiation exposure. For those w orkers designated \200\230classi \201 ed \200\231, personal dosimetry and health surveill ance are required under the Ionizing Radiations Regulations 1999. Such workers are classi \201 ed on the basis of a requirement to work in areas where they may receive at least 30% of the legal, or a lower locally imposed, maximum total dose Appointing a radiation protection adviser (RPA) and radiation protection supervisors (RPS) Arrangement for waste disposal, monitoring exposure, and training on safe work practices and precautions. Control of external exposure Exposure to external ionizing radiation can be reduced by time , distance, and shielding. \200 Time: reduce exposure time to a minimum \200 Distance: arrange work so that the distance from source to worker is as great as possible. The intens ity of point source radiation decreases with increasing distance, obeying the inverse squar e law Shielding of the worker from radiation: advice can be obtained from manufacturers or the RP A on the type and thickness of shielding necessary. This is particularly indicated for pene trating radiation, such as gamma and X-rays. Control of internal exposure This can be reduced by: \200 Containing the source, e.g. in a glove box \200 Good housekeeping and personal hygiene \200 Uses of personal and respi ratory protective equipment, e.g. full face respirator, air hood, or pressurized suit. Classi \201 cation of work areas Work areas are classi \201 ed according to the potential level of exposure: \200 Supervised area: dose rate is less than 7.5 Sv/h, but workers i n that area may receive an effective dose of greater than 1mSv a year \200 Controlled are a: dose rate can exceed 7.5 Sv/h and workers in that area may receive an effective dose of at least 6mSv a year. Relevant legislation \200 Ionizing Radiations Regulations (1999) \200 Ionizing Radiatio n (Medical Exposure) Regulations (2000) \200 Radiation (Emergency Preparedness and Public Information) Regulations (2001). 01_Smedley_Chap01.indd 22 12/31/2012 8:42:05 PM IONIZING RADIATION 4: EXPOSURE CONTROL 23 Further information Cherrie J, Howie R, Sample S (2010). Monitoring for health hazards at w ork , 4th edn. Blackwell Science, Oxford. HSE (2000). Work with ionizing radiation. The Ionizing Radiations Regulations (1999) , appr oved code of Practice and Guidance L121. HSE Books, Sudbury. HSE (2011). Ionizing radiation \200\224radiation protection. HSE, Sudbury. Available at: M http://www. hse.gov.uk/radiation/ionizing/index.htm Health Protection Agency (HPA) website. Available at: M http://www.hpa.org.uk/ProductsServi ces/ Radiation/ NRPB (1998). Living with Radiation , 5th edn. NRPB, Chilton. 01_Smedley_Chap01.indd 23 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 24 Non-ionizing radiation 1: Electromagnetic \201 elds Electromagnetic \201 elds (EMF) rad iation does not have suf \201 cient energy to break the bonds that hold molecules in cells together, and so it does not produce ionization of matter. Effects on the body depend on t he fre- quency and magnitude of EMF. Static electric \201 elds build up charge on the sur face of the body. Magnetic \201 elds can induce \202 ows of electric current in the bod y. Radiofrequency (RF) radiation is partially absorbed, penetrating a short distance into t issues, and can give rise to localized heating. Sources of exposure (occupational and environmental) Static and extremely low-frequency \201 elds (ELF) \200 Electrical power lines \200 Household electrical appliances \200 Electrical transportation \200 Welding. High-frequency or radiofrequency \201 elds (RF ) \200 Radar \200 Radio and television broadcast facilities \200 Mobile telephones an d their base stations \200 Induction heaters \200 Anti-theft devices. Health effects of electromagnetic frequency ELF have been classi \201 ed by the International Agency for Research on Cancer (IARC) 1 a s a possible carcinogen for childhood leukemia in humans, but have not been given a carcino gen notation for any other cancer. The evidence for childhood leukemia is inconclusive and there could be other explanations for the association with ELF. While until recently the balance of evidence has suggested that there are no important heal th effects from RF, IARC has also classi \201 ed this type of EMF as a possible human carc inogen (2B) for glioma. (cid:2) There is currently a high level of public interest and debate regarding exposure to RF (in particular mobile telephones and masts) and the focus of research is on the health effects of long-term low-level exposure. The Interphone study, co-ordinated by IARC, has ye t to show any de \201 nite evidence of public health risk. 1 World Health Organization International Agency for Research on Cancer. Available at: M ht tp:// www.iarc.fr/ 2 International Commission on Non-ionizing Radiation Protection. Available at: M http://www . icnirp.de/what.htm 01_Smedley_Chap01.indd 24 12/31/2012 8:42:05 PM NON-IONIZING RADIATION 1: ELECTROMAGNETIC FIELDS 25 Exposure guidelines Countries set their own exposure standards for EMF, the majority of whi ch are based on the International Commission on Non-ionizing Radiation Protection (ICNIRP). 2 These follow the precautionary principle in setting separate limits for occupational and public exposure. They cover frequen- cies in the range 0 \200\223300GHz and are based on s hort-term acute exposure. In the UK the National Radiological Protection Board (NRPB) (now part of the Health Protection Agency (HPA)) has de \201 ned exposure limits (see b p. 25, Further reading and guidance). Exposure control Elimination is not usually possible. Control measures include: \200 Effe ctive enclosure and re \202 ective screens \200 Control by distance from source \200 P ersonal protective equipment. Relevant legislation Directive 2004/40/EC on the minimum health and safety requirements reg arding the exposure of workers to the risks arising from physical agents (electromagnetic \201 elds). In 2006, it was decided to postpone this Directive until 2012 to permit furthe r consultation. M http://www.hse.gov.uk/ radiation/nonionising/l184emf.pdf Further reading and guidance HPA (2004 ). Advice on Limiting Exposure to Electromagnetic Fi eld (0 \200\223300 GHz) . Volume 15 No.2. Available at: M http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1194947415497 Independent Expert Group on mobile phones (2000). Mobile Phones and health . IEGMP, c/o HPA , Chilton. International Commission on Non-ionizing Radiation Protection (ICNIRP) (2012). M http://www . icnirp.org/ World health Organization (2002). Establishing a dialog on risks from electromagnetic \201 elds . WHO, Geneva. M http://www.who.int/peh-emf/publications/risk_hand/en/index.html The International EMF Project has established a worldwide database of standards. M http://w ww. who.int/peh-emf/standards/en/ 01_Smedley_Chap01.indd 25 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 26 Non-ionizing radiation 2: Optical radiation Relevant legislation The Control of Arti \201 cial Optical Radiation at Work Regulations (2010) aim to protect workers from risks from va rious sources, such as UV light (excluding sunlight) and lasers. The regulations distinguis h between \200\230safe sources \200\231, such as most forms of visible light, and \200 \230hazardous sources \200\231, such as high intensity ultra-violet and laser sources. Ther e are require- ments to consider alternative sources, undertake training and use control me asures. Hazardous light sources Hazardous sources of light that present a risk of harming t he eyes and skin of worker where control measures are needed include: \200 Metal working: welding and plasma cutting \200 Hot processes: furnaces, hot metals /glass \200 Motor vehicle repairs: UV curing of paints and welding \200 Pharmaceutical and research: UV ste rilization and induced \202 uorescence \200 Printing: UV curing of inks and paints \200 Medical and cosmetic treatment: UV and blue light therapies, laser surgery (Class 3B and 4 lasers), intense pulsed light (IPL) Industry and research: use of Class 3B and Class 4 lasers as de \201 ned in BS EN 60825 \200\2231 (2007) Any Risk group 3 lamp or lamp systems as de \201 ned in BSEN 62471 (2008), e.g. professional projections systems. Control measures \200 Use alternative safer light sources \200 Engineering measures: au tomation, controlled areas, remote control, screening, interlocks Use \201 lters, remote viewing and time delays \200 Protect others using screens/curtai ns/restricted access to hazardous areas Provide personal protective equipment, e.g. coveralls, goggles, face-shields, gloves Provide information and training on safe use and best practice \200 Display safety and wa rning signs \200 Monitor use of control measures. 2 If any workers are over-exposed, e.g. damage to skin and eyes provide medical examination and follow-up health surveillance. 01_Smedley_Chap01.indd 26 12/31/2012 8:42:05 PM NON-IONIZING RADIATION 2: OPTICAL RADIATION 27 Ultraviolet Subtypes Ultraviolet light is divided into three types, according to wavelength . Only UVA and UVB from the sun affect humans as UVC is absorbed by the earth \200\231s atm osphere. \200 UVA: 315 \200\223400nm \200 UVB: 280 \200\223315nm \200 UVC: 100 \200 \223285nm. Sources of exposure (occupational and environmental) \200 Welding \200 Print ing \200 Germicidal and mercury lamps \200 Spectroscopy \200 External work (sunlight) . Health effects \200 Skin erythema/burn \200 Premature skin ageing \200 Cataract \200 Photokeratitis \200 Photosensitive and phototoxic reactions (associated with extern al or internal exposure to chemical agents, or skin or systemic diseases) \200 Skin cance r (basal and squamous types are associated with prolonged sun exposure) Bene \201 ts, from Vitamin D production and improvement in some conditions, such as psoriasis. Control measures \200 Limit exposure time to sunlight, especially in the middle of the da y \200 Have shaded areas available for breaks \200 Use suitable clothing and hats to pr otect the skin \200 Use sun protection creams \200 Provide training to workers includin g the above as well as on maintenance of hydration and observation of the skin for suspicious lesions. Laser See b p. 28, Non-ionizing radiation 3: Laser. Further information HSE (2010). Control of arti \201 cial optical radiation at work regula tions . HSE, Sudbury. HSE (2010). Guidance for employers on the control of arti \201 cial optical radiation at work regulations . HSE, Sudbury. Available at: M http://www.hse.gov.uk /radiation/nonionising/employers-aor.pdf 01_Smedley_Chap01.indd 27 12/31/2012 8:42:05 PM CHAPTER 1 Physical hazards 28 Non-ionizing radiation 3: Laser Characteristics \200 Laser radiation has unique propertie s: monochromatic, coherent, bright, high irradiance, and focused to deposit intense energy on small surfaces Lasers can be operated in two major modes: pulsed and continuous wave Lasers are grouped into 7 classes: the higher the class, the greater the potential for harm. Health effects \200 Visible and IR-A laser beams can be focused to create very high intensity exposures on the retina. The effects depend on a number of factors including the wavelength, power, and pulse duration and beam geometry Laser beams produce biological damage by thermal burns and photochemical injuries. Visible and IR-A lasers produce retinal damage \200 The retina is most at risk; thermal and photochemical damage may also occur. \200 inadvertent re \202 ections must be avoided so that beams are not redirected into safe zones a classi \201 cation system for lasers has been developed to ensure safe use (summary shown in Box 1.2) training programs are required for users of class 3 and 4 lasers. Medical surveillance is n ot required by legislation, although has been recommended with the use of class 3B and 4 la sers the ACGIH publishes threshold limit values (TLV) standards for lasers emissions (ocular and skin exposures) for IR, UV and light exposure arising from viewing a laser beam. Controls Controls applied to different laser devices are shown in Box 1.2. Engineering The main engineering control is enclosure, often in the form of inter- locked r ooms. Remote interlocks can make up safety chains covering a large area. Administrative Adm inistrative controls are used during set up and maintenance. These include designated zones , authorization, and warning signs. Personal protective equipment Laser protective goggles must be selected to ensure that they are of appropriate optical density for the type (wavelength) of radiation encoun- tered an d its severity. Lenses are glass or plastic. Glass lenses are heavier, but offer more resis tance to direct strikes and let through more light. Glass is often used when average laser power exceeds 100mW. 01_Smedley_Chap01.indd 28 12/31/2012 8:42:06 PM NON-IONIZING RADIATION 3: LASER 29 Box 1.2 Laser safety classi \201 cation and required controls Class 1 \200 Safe under re asonably foreseeable conditions of operation \200 Protection measures not necessary, pers onal protective equipment (PPE) not required. Class 1M \200 Safe for naked eye, may be hazardous if the user employs optics \200 Prev ent use of magnifying, focusing, or collimating optics \200 PPE not required. Class 2 \200 Safe for short exposures, eye protection afforded by aversion response Follow manufactures instructions for safe use \200 Do not stare in to beam \200 PPE not required. Class 2M \200 Safe for naked eye for short exposures, may be hazardous if the user employs optics Do not stare in to beam, prevent use of magnifying, focusing or \200 Training recommended , PPE not required. Class 3R \200 Risk of injury is relatively low, but may be dangerous for improper collimating optics use by trained by untrained person Enclosed \200 Prevent direct eye exposure \200 Training required \200 PPE may be requ ired subject to \201 ndings of risk assessment. Class 3B \200 Direct viewing is hazardo us \200 Enclosed and interlock protected \200 Prevent eye and skin exposure to the beam . \200 Training and PPE required. Class 4 \200 Hazardous for eye and skin; \201 re ha zard \200 Enclosed and interlock protected \200 Prevent eye and skin exposure from dire ct and diffuse re \202 ection of \200 Training and PPE required. the beam 01_Smedley_Chap01.indd 29 12/31/2012 8:42:06 PM CHAPTER 1 Physical hazards 30 Thermal environment 1: thermal balance and instrumentation Heat stress Heat stress occurs w hen the body \200\231s means of controlling internal tem- perature starts to fail. Operatio ns involving high air temperatures, radiant heat sources, high humidity or strenuous physic al activities have a high potential for inducing heat stress. Heat balance \200 The body core temperature must be regulated to remain typically at 37 0.5 C. Below 31 C leads to loss of consciousness and death. Above 43 C le ads to failure of the thermoregulation mechanism \200 Heat balance between the human body and its surroundings can be expressed as the equation M = K C R \200\223 E where M is the rate of metabolic heat production (see Table 1.3), K , C , and R are gain or loss of heat by conduction, convection, and radiation, respec- tively, and E is the evapor ative heat loss from skin and respiratory tract. \200 The heat balance is affected by wor k performed and the rate of change in the store of heat in the body. Health effects \200 Exposure to high temperature: heat stroke, heat syncope, heat exhaustion, heat fatigue and prickly heat, cataract, susceptibility to other disease (e.g. cardiovascular) Exposure to low temperature: hypothermia is a condition of low core temperature, and is clinically de \201 ned as a deep body temperature below 35 C. Occupations at risk Work activities that may lead to heat stress include: handling molten m etal, metal re \201 ning, glass-making, boiler and furnace maintenance, mining and tunneli ng, \201 re \201 ghting, and outdoor work in hot climates. Parameters and instruments fo r heat stress The following four environmental parameters must be assessed: \200 air temp erature \200 air velocity \200 radiant temperature \200 relative humidity. 01_Smedley_Chap01.indd 30 12/31/2012 8:42:06 PM THERMAL ENVIRONMENT 1 31 Instruments for measuring individual environmental parameters include: \200 Dry bulb ther mometers or electric thermometers: measure air temperature Wet bulb thermometer: dry bulb covered in a clean cotton wick wetted with distilled water Psychrometers: consist of wet and dry bulb thermometer mounted in a frame. There are two ty pes \200\224the sling and the aspirated. Used to determine the relative humidity Globe thermometer (mercury-in-glass thermometer with its bulb in the center of a matt black sphere or globe): used to measure radiant temperature Kata thermometer: used for measuring air velocities less than 0.5m/s. Integrating electroni c heat stress monitors \200 Static instruments: provide a single value for wet bulb globe temperatures (WBGT) and air velocities (Fig. 1.2) Personal heat stress monitors (Fig. 1.3): signals from various sensors including heart rate and temperature fed into a data logger, which calculates a strain index. The monitor can b e set for different age ranges and clothing. An audible alarm, indicating if preset warning and action levels are exceeded, is usually \201 tted. Table 1.3 Metabolic rates for activities Class Mean metabolic rate (Wm 2 ) Example Resting 65 Resting Low 100 Standing Moderate 165 Sustained hand/arm work High 230 Intense work Very high 290 Very intense to maximum activity 01_Smedley_Chap01.indd 31 12/31/2012 8:42:06 PM CHAPTER 1 Physical hazards 32 hs-32 ARCA HEAT STRESS MONITOR on off Stlness Stetup Fig. 1.2 Electronic integrating heat stress monitor. Fig. 1.3 Personal heat stress monitor. 01_Smedley_Chap01.indd 32 12/31/2012 8:42:06 PM This page intentionally left blank CHAPTER 1 Physical hazards 34 Thermal environment 2: Assessment of the thermal environment A number of heat stress indice s have been developed for different indus- tries, with the aim of preventing the deep body temperature from exceed- ing 38 C. Classi \201 cation of heat stress indices Empirical and direct indices Wet bulb temperatur e (WB), effective temperature (ET), corrected effec- tive temperature (CET), WBGT. Analytic al indices Required sweat rate, heat stress index, predicted 4h sweat rate. Wet bulb globe temperature The WBGT is the most widely accepted index for assessment of heat in industry a nd published as British Standard BS EN 27243 and also in the ACGIH threshold limits values. WBGT (expressed in temperature units) is calculated as follows: For indoor use, WBGT = 0.7 WB + 0.3 GT For outdoor use, WBGT = 0.7 WB + 0.2 GT + 0.1 DB where WB is natural wet bulb temperature); GT is the globe thermom- eter temperature ( C), and DB is the dry bulb temperature ( C). Table 1.4 shows reference values of WBGT related to a maximum rec- tal temperature of 38 C for different metabolic rates and state of acclima- tization. The reference values assume the individual is \201 t, normally clothed with adequate water and salt intake. Example In a foundry with still air, a worker is acclimatized and estimated to be working a t 240W/m 2 . Air temperature = 25 C, globe temperature = 27 C, natural wet bulb = 18 C, WBGT = 0.7(18) + 0.3(25) = 20.1 The reference WBGT value of 25 C for this scenario is not exceeded, i.e. heat stress in no t a risk in this environment. When the WBGT reference values are exceeded a more accurate heat stress estimate can be obt ained using, for example, the required sweat rate (BS EN12515). When performing physiologic al monitoring (core tem- perature, heart rate, sweat rat, etc.) use standard ISO 9886. 01_Smedley_Chap01.indd 34 12/31/2012 8:42:06 PM THERMAL ENVIRONMENT 2 35 Acclimatization Acclimatization is a set of physiological adaptations. Full heat acclimatiz a- tion requires up to 3wks of physical activity under the heat stress condi- tions expecte d in the work environment. During acclimatization, the ability of the body to sweat is incr eased and amount of sweat produced is also increased. Salt content of sweat declines avoidi ng sodium de \201 ciency. Table 1.4 WBGT reference values from BS EN 27243 Metabolic rate, M WBGT reference value Metabolic Rate class Related to a unit skin surface area (Wm 2 ) Total (for a mean skin surface area of 1.8m 2 ) (W) M \211 117 Person acclimatized to heat ( o C) Person not acclimatized to heat ( o C) 0 (resting) M \211 65 1 33 65<M \211 130 117<M \211 234 30 130<M \211 200 234<M \211 360 28 200<M \211 26 0 360<M \211 468 No 32 29 2 26 3 Sensible air move ment No Sensible air move ment Sensible air move ment sensible air move ment 25 26 22 23 4 M>260 M>468 23 25 18 20 Note: BS EN ISO 27423 does not provide correction to WBGT values for different types of per sonal protective equipment (PPE). See M http://www.hse.gov.uk/temperature/index.htm for est imated increase in metabolic when wearing personal protective equipment. Risk control: reducing heat strain \200 Planning of work: e.g. maintenance work \200 Mo difying the environment: reduce process heat, improve ventilation, evaporative cooling, shield radiant heat sources Worker: medical pre-selection, acclimatization, report symptoms \200 Managerial: monitor heat stress conditions, develop work \200\223rest regimes, training and supervision, selection of appropriate controls Protective clothing: ice-cooled jackets, air-cooled suits. Relevant legislation \200 Workplace (Health, Safety and Welfare) Regulations (1992) \200 Management of Health and Safety at Work Regulations (1999). Further information American Conference of Industrial Hygienists (ACGIH) (2011). Threshold limit values for chemical substances and physical agents and biological exposure indices. ACGIH, Cincinnati. British Occupational Hygiene Society (BOHS) (1996). The Thermal Environment, BOHS Technical Guide No.12, 2nd edn. BOHS, Derby. Parsons KC (2003). Human thermal environment, 2nd edn. Taylor & Francis, London. Youle A (2 005). The thermal environment. In: Harrington JM, Gardener K, eds, Occupational Hygiene, 3r d edn. Blackwell Science, Oxford. Available at: M http://www.hse.gov.uk/tempera- ture/index .htm indices 01_Smedley_Chap01.indd 35 12/31/2012 8:42:07 PM CHAPTER 1 Physical hazards 36 Thermal environment 3: Assessment of cold workplaces Health effects and occupations \200 The p physiological responses to cold exposure are peripheral vasoconstriction and increase in metabolic heat production by shivering Effects of cold include hypothermia (below 35 C), localized tissue damage, and adverse eff ects on performance at work. Outdoor (construction, telecommunications, maintenance of elec trical power lines, agricultural and forestry, \201 shing industry), indoor (cold stores, meat processing) also inland and offshore work. Risk assessment \200 ISO 1574 (2008) provides methodology and practical tool for assessin g and managing cold risk in the workplace. It includes checklists and questionnaires to ide ntify individuals at risk The main climate factors for cold stress are air temperature and air speed. As the differen ce between skin and ambient temperature increases and/or the air speed increases, the rate of heat loss from exposed skin increases A wind chill index (equivalent chill temperature) can be calculated has for different combi nations of air temperature and speed (see b p. 37, Calculating the Wind Chill Index and int erpretation of values) \200 The equivalent chill temperature is used when estimating the combined cooling effect of wind and low air temperature on exposed skin or when determining clothing insulation requirements to maintain core temperature above 36 C. The model is ba sed on exposed \202 esh, but is a useful \201 rst approximation of cold stress. Risk control \200 For exposed skin, continuous exposure should not be permitted when the equivalent chill temperature is \200\22332 C. If air temperature falls below 16 C for sedentary, 4 C for light, or \200\2237 C for mo derate work, gloves should be used by workers \200 If \201 ne work is performed with ba re hands for more than 20min in an environment below 16 C, provision should be made to keep hands warm Total body protection is required if work is performed in an environment at or below 4 C The ACGIH recommends that protective measures should be introduced when air temperature is less than 5 C. The equation shown here can be used to e stimate the amount of clothing insulation (1 clo) required for a speci \201 c task in a gi ven air temperature ( T in C) and metabolic rate ( M in W): clo = 11.5(33 \200\223 T)/M When cold surfaces below \200\2237 C are within reach, a warning should be given to prevent inadvertent contact with bare hands. 01_Smedley_Chap01.indd 36 12/31/2012 8:42:07 PM THERMAL ENVIRONMENT 3 37 Calculating the Wind Chill Index and interpretation of values \200 The Wind Chill Index ( Twc) can be calculated using the equation: Twc = 13.12 + 0.6215.Ta \200\22311.37.v0.16 + 0.3965.Ta.v0.16 where T a is the air temperature ( C) and V air speed (km/h). Example If the dry temperature is \200\223 22 C at 16 km/h then the wind chill factor = \200\223 32 C Twc values ( C) \200\22310 to \200\22324 (uncomfortably cold), \200\22325 to \200\2233 4 (very cold, risk of skin freezing), \200\22335 to \200\22359 (exposed skin may freeze within 10 min), below \200\22360 (exposed skin may freeze in 2min). Relevant legislation \200 Workplace (Health, Safety and Welfare) Regulations (1992) \200 Management of Health and Safety at Work Regulations (1999). Further information ISO 15743 (2008). Ergonomics of the thermal environment \200\224Cold workplaces \200\224Risk assessm ent and management . ISO 11079 (2007). Evaluation of the thermal environment \200\224Determination of required c lothing insula- tion (IREQ) . BS EN 511 (2006). Protective gloves against cold . 01_Smedley_Chap01.indd 37 12/31/2012 8:42:07 PM CHAPTER 1 Physical hazards 38 Thermal environment 4: Thermal comfort De \201 nition \200 Thermal comfort describes the person \200\231s psychological state of mind and is de \201 ned as \200\230that conditio n of mind which expresses satisfaction with the surrounding thermal environment \200\231 (B S EN ISO 7730). Thermal comfort depends on a range of environmental (air temperature, humidity, air movement, and radiant heat) and personal factors (clothing insul ation and metabolic heat). In workplaces, thermal discomfort may only occur when heating ve ntilation and air conditioning systems either break down or do not work as intended. \200 Thermal comfort can affect overall morale. Complaints may increase and productivity may fa ll. Most problems arise when individuals are not able to adapt to their work environment. L ocalized discomfort can also occur, e.g. due to vertical temperature gradients. Assessment of thermal comfort \200 International Standards (BS EN ISO 7730 and BS EN ISO 10551) provide methods for predicting the general thermal sensation and degree of discomfor t (thermal dissatisfaction) in indoor environments. The methods for the objective assessmen t of the thermal environment included in these standards are based on those proposed by Fan ger (1970) 1 Thermal comfort is determined using calculations of predicted mean vote (PMV) and predicted percentage dissatis \201 ed (PPD) The PMV is an index that predicts the mean value of the votes of a large group of persons o n the 7-point thermal sensation scale (Table 1.5) and can be calculated for different metab olic rates, air temperature, air velocity, clothing insulation, and air humidity. Combinati ons of these parameters, which on average will provide a thermally neutral sensation, can b e determined The PPD establishes a quantitative prediction of the percentage of thermally dissatis \201 ed people, i.e. those who will vote hot, warm, cool, or cold on th e 7-point thermal sensation scale The 7-point thermal sensation scale can also be used to assess and compare the actual and desired thermal sensations. Controlling the thermal environment A combination of engineering and administrative are req uired: \200 Work planning: location of work station and scheduling of work and breaks Assess the type of heating system (hot air based, combined heat and ventilation, under \202 oor heating, overhead heating) Air movement: consider the type and location of fan(s), reduce draft discomfort by directing ventilation or air movement Air conditioning: determine whether the unit controls air movement and humidity as well low ering air temperature. Air distribution from units should be uniform throughout the workpla ce 01_Smedley_Chap01.indd 38 12/31/2012 8:42:07 PM THERMAL ENVIRONMENT 4 39 Assess the need for thermal insulation: insulation type present and its effectiveness