Monitoring Occupational Environment
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This document provides an overview of occupational health training courses focusing on assessment of workplace hazards. It discusses measuring physical hazards like noise, light, heat and thermal environment. Noise is measured using a sound level meter in decibels while light is measured in lux units using a lux meter. Heat stress and strain are also explained. Methods for measuring chemicals hazards like vapors, fumes and dust are outlined. Sampling techniques including grab, short term and long term sampling are covered. Hygiene standards used to evaluate exposure levels like TLVs are also mentioned.
Monitoring Occupational Environment
- 1. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Occupational Health Courses Dr. Ahmed-Refat Professor of Occupational Medicine Tibah University, KSA, March ,2012 www.SlideShare.net/AhmedRefat 1- Assessment of Work Place Hazards: Measuring Tools and Principles Introduction: Occupational Hygiene: "The discipline of anticipating, recognizing, evaluating and controlling health hazards in the working environment with the objective of protecting worker health and well-being and safeguarding the community at large. 1
- 2. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Components of Occupational Hygiene: — —ANTICIPATION – this involves identifying potential hazards in the workplace before they are introduced. — —RECOGNITION - this involves identifying the potential hazard. — —EVALUATION of the extent of exposure to hazards in the workplace. This often involves measurement of the personal exposure of a worker to the hazard in the workplace, and —assessment of the data in terms of recommended occupational exposure limits (OELs), where such criteria exist. Controlling health hazards in the working environment. 2
- 3. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat I- Measuring of Physical Hazards A- Noise Basic Concepts : Sound is fluctuations in pressure above and below the ambient pressure of a medium that has elasticity and viscosity. The medium may be a solid, liquid, or gas. Sound is the auditory sensation evoked by the oscillations in pressure . Noise = unwanted sound, Sound perceived by the ear results from fluctuations ( Frequency – cycle per second - Hz ) the pressure ( Intensity- Power – Loudness –Energy – dB ) of the air. 3
- 4. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Decibel: The decibel ( dB) is a dimensionless quantity. Unit of Sound/ Noise intensity 4
- 5. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat dB weighting: • A-weighting’, or dB(A), is used to measure average noise levels as it approximates the sensitivity of the human ear at low noise levels. This is typically used to assess for the potential of hearing loss ‘C-weighting’, or dB(C), is used to measure peak, impact or explosive noises. This weighting is used to determine suitable personal hearing protection equipment in high noise environments 3dB change in noise level results in a doubling of the noise Workplace Noise Levels 5
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- 7. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat B- Light Basic Concepts: Measuring of Workplace Illumination Light meter / 'Lux' meter). 7
- 8. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat What is a light meter? A light meter measures the level (amount) of visible light (illumination) in a given area tested. Illumination is expressed in units of lumens per square meter LUX (metric) and lumens per square ft. Foot candles/ Fc (English). Convert Foot candles, LUX, and Lumens: • Multiply Foot candles by 10.76891 to convert to LUX • Multiply LUX by 0.09290304 to convert to Foot candles • Foot candles = Lumens per sq. ft. Sun = 107,527 Lux Full day light = 10,752 Lux Full moon = 108 Lux Work place Adequate Light ( office ): • General background 160–240 Lux • Routine office work (typing, filing) 400 Lux • Work with poor contrast (proof reading) 600 Lux. 8
- 9. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Minimum Illumination Intensity on Objects of Work 9
- 10. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat C- Heat Basic Concepts: HEAT STRESS “The net heat load to which a worker may be exposed from the combined contributions of metabolic cost of work, environmental factors (ie air temperature, humidity, air movement and radiant heat exchange) and clothing requirements.” HEAT STRAIN “The physiological impact of heat stress on the body, as expressed in terms of changes in tissue temperatures and compensatory changes in the activity of physiological systems (sweat rate, heart rate, skin blood flow).” Heat strain = “The overall physiological response resulting from heat stress.” 11
- 11. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Temperature Levels and its effects 46.5°C Highest recorded survivable core temperature 43°C Tissue damage (brain, liver) 41°C Cessation of sweating 39°C The threshold of hyperthermia 36.8°C Normal core temperature 35°C The threshold of hypothermia 33°C Impaired muscle function, introversion, loss of mental alertness 30°C Cessation of shivering and then unconsciousness 28°C Possible ventricular fibrillation 26°C Bradycardia and bradypnoea 24°C Possible death without rewarming 14.4°C Lowest recorded core temperature for a survivor of accidental hypothermia 11
- 12. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Damaging Effects of Heat Exposure >50°C Second-degree burn >45°C Tissue damage 41 – 43°C Burning pain 39 – 41°C Pain 33 – 39°C Skin warmth through to discomfort (hot) 28 – 33°C Thermal comfort 25 – 28°C Cool through to discomfort (cold) 15°C Pain 10°C Loss of skin sensation 5°C Non-freezing cold injury: (time dependent, and can occur between 17 – 0.55°C) <0.55°C Freezing cold injury (frostbite) 12
- 13. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Measuring of Thermal Environment Measurement of air temperature is usually made with one of the following techniques: Mercury-in-glass thermometer Thermocouple Platinum resistance thermometer Thermistor A- Mean Radiant Temperature Measurement of the mean radiant temperature can be derived from the readings of a black globe thermometer. This consists of a hollow black globe usually made of copper (due to its high conductivity) in the centre of which is placed a temperature sensor . 13
- 14. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat B- Humidity • Air contains a certain amount of water vapour • Higher air temperature – more water vapour can be contained in the air • Lower air temperature – less water vapour can be contained in the air The absolute humidity is defined as the mass of water vapour in air per unit volume of air/water vapour mixture and has units of kg m-3. Relative humidity is defined as: “The ratio of the prevailing partial pressure of water vapour to the saturated water vapour pressure.” The “dew point” is the temperature at which the air becomes saturated. Dry & wet Bulb Thermometer • Water evaporating from a surface reduces the temperature of the surface • If the bulb of a thermometer is covered by a damp fabric sleeve water evaporating causes a lower reading - this is termed the wet bulb temperature • The difference between dry bulb temperature and wet bulb temperature can be used to determine relative humidity 14
- 15. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat • At 100% relative humidity no evaporation takes place so the dry bulb temperature and wet bulb temperature will be the same Measuring relative Humidity • One of the most commonly used instruments for determining humidity is the whirling hygrometer, which is also called a sling psychrometer (Figure 5.2). Whirling hygrometer one dry bulb thermometer one wet bulb thermometer - bulb covered with wick dipped into distilled water reservoir air flow (> 4 metres / sec) achieved by ‘whirling’ read wet bulb temperature first, then dry bulb Its operation is relatively simple. The sling psychrometer consists of two thermometers, a wet bulb and dry bulb. A “wick” or “sock” covers one of the thermometers (the “wet” bulb) and should be thoroughly wetted using distilled (de-ionised) water prior to taking any measurements. This involves filling the water reservoir at the end of the psychrometer and may 15
- 16. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat also involve manually wetting the wick. Care should be taken not to contaminate the wick with dirty fingers or water that is not de-ionised. The handle is then unclipped and the psychrometer is swung for at least 20 – 30 seconds. This will allow an air movement to pass over the wet bulb thermometer and initiate evaporation of water from the wick. After 20 – 30 seconds, the aspirated wet bulb temperature is read first (then the dry bulb temperature). These values are noted and the measurements repeated three times. Optimally, the repeated measurements should be within ±1°C of Calculation Psychrometric charts – Charts that inter-relate – vapour pressure (water content) – relative humidity – dry bulb temperature – wet bulb temperature 16
- 17. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Measurement of Air Velocity Air movement across the body can influence heat flow to and from the body and hence body temperature Air velocity can be measured by a number of methods • Vane anemometer – Directional & not accurate at low velocities • Hot-wire anemometer – Directional & inaccurate at low velocities • Kata thermometer – Omni-directional but not suited to conditions where large or rapid variations in air movement occur 17
- 18. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Vane anemometer Hot-wire Anemometer 18
- 19. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Kata Thermometer • Principle of operation – thermometer with large bulb – two marks on stem (3K apart) – heated so that fluid is above higher mark – fixed in monitoring position – allowed to cool – time for fluid to cool to lower mark noted 19
- 20. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Wet Bulb Globe Thermometer 21
- 21. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Wet Bulb Globe Thermometer Calculation of WBGT 21
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- 23. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat II- Chemical Hazards Physical States of chemicals • • Vapour - the gaseous state of a substance which is liquid at 25°C and 760 mm Hg (STP). • Mist - liquid particles, large size generally produced by bubbling, splashing or boiling of a liquid. • Fume - Solid particles produced by condensation from a liquid or a reaction between two gases. The particle size of a fume <1 micron (µm) diameter anything larger is considered a dust particle. • 23
- 24. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat • Dust - particles of solid material in the broad size range of 1 micron to 1 millimetre diameter. Anything of a larger particle size is considered to be grit and will be too heavy to remain airborne. • Aerosol - general term for the dispersions of solid or liquid particles of microscopic size in a gaseous medium e.g. fog, smoke etc. although commonly used to term fine liquid spray (e.g. ‘aerosol can’). Fibre – Solid particulate which are long and thin i.e. have a high aspect ratio of length to breadth. Types of Sampling • Grab • Short term • Long term • Continuous Sampling Pattern • Grab sampling • Task duration sampling • Short period sampling (less than the task duration and sometimes taken consecutively) • Full shift sampling • 24
- 25. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Grab Concentration Time Short Term Concentration Time 25
- 26. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Long Term Concentration Time Continuous Concentration Time 26
- 27. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Sampling for Particulates/Dust Particle Size Distribution 27
- 28. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Particle size Total inhalable dust is the fraction of airborne material which enters the nose and mouth during breathing and is therefore liable to deposition anywhere in the respiratory tract. The particle sizes of total inhalable dust are up to 100 microns. Respirable dust is that fraction that penetrates to the deep lung where gas exchange takes place. The particle sizes of respirable dust are up to 10 microns Breathing Zone As the main route of entry into the body for many substances is via inhalation, it is logical that any estimate of exposure of such substances should be conducted in a location consistent with normal inhalation patterns of workers. By convention, this has been deemed the “breathing zone” . “A hemisphere of 300 mm radius extending in front of the face and measured from the midpoint of a line joining the ears.” 28
- 29. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Elements of a Sampling System 29
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- 31. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Sampling for Gases and Vapours • Active Sampling - i.e. by means of a mechanic/sampling pump method. – Sorbent Tubes • Passive Sampling 31
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- 33. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat 33
- 34. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Indicator Tubes (Gas Grab Sampling) Before ( Left) and after sampling (Right) 34
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- 36. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat HYGIENE STANDARDS By “hygiene standard” we are referring to the level of exposure, via inhalation, that should not cause ill health to a healthy adult when exposed to a contaminant. The results from air sampling can thus be compared against these standards and can be used as a guide to assist in the control of health hazards. Other names for hygiene standards commonly used throughout the world are Threshold Limit Values (TLVs®), Exposure Standards (ES), Occupational Exposure Limits (OEL), Workplace Exposure Limits (WEL). In general all such terminology is interchangeable. The best known list of “hygiene standards” is the Threshold Limit Values (TLVs®) produced by the American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs®) refer to airborne concentrations of chemical substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed, day after day, over a working lifetime, without adverse health effects. 36
- 37. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat There are three types of TLVs® 1. TLV-Time Weighted Average (TLV-TWA) 2. TLV-Short Term Exposure Limit (TLV-STEL) 3. TLV-Ceiling (TLV-C) 4.3.1 TLV-TWA “The TWA concentration for a conventional 8-hour workday and a 40-hour work week, to which it is believed that nearly all workers may be repeatedly exposed, day after day, for a working lifetime without adverse effect.” TLV-STEL “A 15 minute TWA exposure that should not be exceeded at any time during a workday, even if the TWA is within TLV-TWA. The TLV-STEL is the concentration to which it is believed that workers can be exposed continuously for a short period without suffering from: 1. irritation 2. chronic or irreversible tissue damage 3. dose-rate dependent toxic effects, or 4. narcosis of sufficient degree to increase the likelihood of accidental injury, impaired self rescue, or materially reduced work efficiency.” TLV-C “The concentration that should not be exceeded during any part of the working exposure. If instantaneous measurements are not available, sampling should be conducted for the minimum period of time sufficient to detect exposures at or above the ceiling value.” 37
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- 39. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Mixtures When two or more hazardous substances have a similar toxicological effect on the same target organ or system, their combined effect rather than that of either individually, should be given primary consideration. In the absence of information to the contrary, different substances should be considered as additive where the health effect and target organ or systems is the same ie: C1/TLV1 + C2/TLV2 + …… + Cn/TLVn ≤ 1 39
- 40. {{{ Occupational Health Training Courses }}} www. Slideshare.net/AhmedRefat Conversion of PPM to mg/m3 41