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Environmental Conditions Presentation Transcript
1.Setting out Environment of a workspace
2.Environmental Conditions
From the infancy of the discipline, ergonomists realized that our ability to perform work is inextricably linked to the prevailing environmental conditions in the workplace.
When environmental conditions exceed the capabilities of the body's adaptive mechanisms, then performance and health deteriorate, and in extreme situations conditions could even prove fatal.
From the infancy of the discipline, ergonomists realized that our ability to perform work is inextricably linked to the prevailing environmental conditions in the workplace.
When environmental conditions exceed the capabilities of the body's adaptive mechanisms, then performance and health deteriorate, and in extreme situations conditions could even prove fatal.
3.Goal of the ergonomic design
The goal of the ergonomic design of the workplace environment is to create prevailing ambient conditions that are comfortable, acceptable, and do not compromise work performance or worker health.
Modern work environments are constructed to meet various health and safety standards for appropriate thermal, visual, aural, and other conditions.
4.Ergonomic design of the work environment conditions
The goal of the ergonomic design of the workplace environment is to create prevailing ambient conditions that are comfortable, acceptable, and do not compromise work performance or worker health.
Modern work environments are constructed to meet various health and safety standards for appropriate thermal, visual, aural, and other conditions.
4.Ergonomic design of the work environment conditions
5.Roles of Ergonomist
The ergonomist can play two important roles:
Setting the environmental conditions limits for acceptable human performance.
Bringing a systems perspective to the design process to assess the interplay between the different designed environmental conditions and the nature of the work tasks, the work technology, and the characteristics of the workers.
The ergonomist can play two important roles:
Setting the environmental conditions limits for acceptable human performance.
Bringing a systems perspective to the design process to assess the interplay between the different designed environmental conditions and the nature of the work tasks, the work technology, and the characteristics of the workers.
6.Different Types of Environmental Conditions Measurements
Thermal Conditions Measurement
Cold Stress Indices
Heat Stress Indices
Thermal Comfort Indices
Indoor Air Quality: Chemical Exposures
Indoor Air Quality: Biological/Particulate
7.Thermal Conditions Measurement
Thermal Conditions Measurement
Cold Stress Indices
Heat Stress Indices
Thermal Comfort Indices
Indoor Air Quality: Chemical Exposures
Indoor Air Quality: Biological/Particulate
7.Thermal Conditions Measurement
8.Objective Heat-Exchange Analysis
Metabolic activity-
For a body at rest, this is the amount of energy needed for the body’s basic functions.
Metabolic activity increases when the body is working.
9.The ratio between this external work and the total energy consumed is the efficiency with which the body performs the work.
In the cold, shivering can produce additional heat, increasing metabolic rate and heat production up to fourfold.
10.Pathways for heat loss, from the body and environment
Metabolic activity-
For a body at rest, this is the amount of energy needed for the body’s basic functions.
Metabolic activity increases when the body is working.
9.The ratio between this external work and the total energy consumed is the efficiency with which the body performs the work.
In the cold, shivering can produce additional heat, increasing metabolic rate and heat production up to fourfold.
10.Pathways for heat loss, from the body and environment
11.Measurement of Relevant Factors in Heat Exchange
12.
External parameters that need to be assessed to determine heat or cold stress levels or comfort conditions include:
• Temperature
• Air humidity
• Air speed
External parameters that need to be assessed to determine heat or cold stress levels or comfort conditions include:
• Temperature
• Air humidity
• Air speed
13.Temperature
As temperature increases, body heat loss by convection, conduction, and radiation decreases.
The overall effect of temperature can be assessed by measuring three relevant properties:
Air temperature (ta)
2. Mean radiant temperature (tr)
3. Surface temperature (ts)
As temperature increases, body heat loss by convection, conduction, and radiation decreases.
The overall effect of temperature can be assessed by measuring three relevant properties:
Air temperature (ta)
2. Mean radiant temperature (tr)
3. Surface temperature (ts)
14.Air Temperature
Air Temperature can be measured by a conventional alcohol-filled thermometer or by an electronic thermometer.
A (polished) shield is used in combination with a device to suck air.
Eg. Blowing could add heat from the fan motor.
Air Temperature can be measured by a conventional alcohol-filled thermometer or by an electronic thermometer.
A (polished) shield is used in combination with a device to suck air.
Eg. Blowing could add heat from the fan motor.
15.Sensor range/accuracy: to measure comfort: 10 to 40ºC/±0.5ºC; to measure stress: –40 to +120ºC/ outside comfort range ±1ºC; desirable accuracy ±0.2ºC.
16.Mean Radiant Temperature
Mean Radiant Temperature is the mean temperature of all walls and objects in the space (including sky outdoors).
When mean radiant temperature exceeds skin temperature heat transfers from the environment to the skin.
Eg. in steel mills, or in work in the sun.
Mean Radiant Temperature is the mean temperature of all walls and objects in the space (including sky outdoors).
When mean radiant temperature exceeds skin temperature heat transfers from the environment to the skin.
Eg. in steel mills, or in work in the sun.
17.Surface Temperature
Surface Temperature is measured with special sensors that ensure a good contact with the surface while insulating the sensor from the environment, or with a noncontact infrared sensor.
With a contact sensor, the conduction between surface and sensor must be much higher than that from the sensor to the environment, and sometimes conductive paste helps.
Surface Temperature is measured with special sensors that ensure a good contact with the surface while insulating the sensor from the environment, or with a noncontact infrared sensor.
With a contact sensor, the conduction between surface and sensor must be much higher than that from the sensor to the environment, and sometimes conductive paste helps.
18.surfaces with very low conductivity (e.g., wood) may yield false values, and in such cases a noncontact infrared sensor is better.
Sensor ts range/accuracy: comfort: 0 to 50ºC, ±1ºC; stress: –40 to +120ºC, between –10 and +50ºC: ±1ºC, below –10ºC and above +50ºC: linear increase from 1 to 3.5ºC and 4.5ºC, respectively, to range limit; desirable accuracy comfort: ±0.5ºC; desirable accuracy for stress: ±0.5ºC
19.Air Humidity
The amount of moisture present in the environmental air determines whether moisture (sweat) in vapor form flows from the skin to the environment or vice versa.
Relative humidity can be measured with hair hygrometers, Electronic sensors, Dewpoint sensors.
Dewpoint sensors is very accurate, but costly.
Sensor ts range/accuracy: comfort: 0 to 50ºC, ±1ºC; stress: –40 to +120ºC, between –10 and +50ºC: ±1ºC, below –10ºC and above +50ºC: linear increase from 1 to 3.5ºC and 4.5ºC, respectively, to range limit; desirable accuracy comfort: ±0.5ºC; desirable accuracy for stress: ±0.5ºC
19.Air Humidity
The amount of moisture present in the environmental air determines whether moisture (sweat) in vapor form flows from the skin to the environment or vice versa.
Relative humidity can be measured with hair hygrometers, Electronic sensors, Dewpoint sensors.
Dewpoint sensors is very accurate, but costly.
20.Air humidity is expressed as relative humidity,
21.Air Speed
The magnitude of air movement (Va) and its direction and turbulence affects both convective and evaporative heat losses, and heat exchange increases with increasing wind speed.
Air speed can be measured using a vane or cup anemometer.
The magnitude of air movement (Va) and its direction and turbulence affects both convective and evaporative heat losses, and heat exchange increases with increasing wind speed.
Air speed can be measured using a vane or cup anemometer.
22.In a cool environment, the body cools faster in the presence of wind.
In an extremely hot, humid environment, it will heat up faster.
In a very hot but dry environment, it will promote dry heat transfer toward the body, but will also increase evaporative heat loss from the body.
In an extremely hot, humid environment, it will heat up faster.
In a very hot but dry environment, it will promote dry heat transfer toward the body, but will also increase evaporative heat loss from the body.
23.Sensor v range/accuracy: comfort: 0.05 to 1 msec–1 ± (0.05 + 0.05v) msec–1; stress: 0.2 to 20 msec–1 ± (0.1 + 0.05v) msec–1; response time (90% of final value reached in this time): comfort <0.5 sec, desirable <0.2 sec (for measurement of turbulence intensity).
24.Personal Parameters
Some thermal comfort and stress assessment methods require information on clothing insulation and metabolic heat production, are:
1. Clothing Insulation
2. Metabolic Rate
Some thermal comfort and stress assessment methods require information on clothing insulation and metabolic heat production, are:
1. Clothing Insulation
2. Metabolic Rate
25.Clothing Insulation
Clothing resists heat and moisture transfer between skin and environment.
This can protect against extreme heat and cold, but it can also hamper heat loss during physical effort.
Clothing insulation is expressed either as total insulation (It, includes surface air layer) or so-called intrinsic insulation (Ict, clothing with enclosed air layers only).
26.Metabolic Rate
All metabolic energy is released as heat in the body.
It can be measured using indirect calorimeter (measuring oxygen uptake).
Metabolic rates for a large number of activities can be estimated using standard tables describing activities, professions, postures, etc.
Clothing resists heat and moisture transfer between skin and environment.
This can protect against extreme heat and cold, but it can also hamper heat loss during physical effort.
Clothing insulation is expressed either as total insulation (It, includes surface air layer) or so-called intrinsic insulation (Ict, clothing with enclosed air layers only).
26.Metabolic Rate
All metabolic energy is released as heat in the body.
It can be measured using indirect calorimeter (measuring oxygen uptake).
Metabolic rates for a large number of activities can be estimated using standard tables describing activities, professions, postures, etc.
27. Subjective Methods
28.Cold Stress Indices
29.Methods to Analyze Cold Strain
1. Wind-Chill Indices
2. Required Clothing Insulation
3. Physiological Measurement
4. Thermal Sensation
5. Cold Strain Index
6. Conductive Heat Loss
1. Wind-Chill Indices
2. Required Clothing Insulation
3. Physiological Measurement
4. Thermal Sensation
5. Cold Strain Index
6. Conductive Heat Loss
30.Wind-Chill Indices
The original wind-chill index (WCI) was developed by Siple and Passel (1945) based on their empirical experiments.
WCI gives the amount of heat loss in a given combination of ambient temperature and air movements. It also gives a temperature equivalent in calm conditions.
The original wind-chill index (WCI) was developed by Siple and Passel (1945) based on their empirical experiments.
WCI gives the amount of heat loss in a given combination of ambient temperature and air movements. It also gives a temperature equivalent in calm conditions.
31.Wind-chill index is not a temperature, but it expresses human sensation (equivalent temperature).
Considering the risk of frostbite, W can be interpreted as follows:
1. Risk of frostbite in prolonged exposure (30 minutes) at –28°C
2. Frostbite possible in 10 minutes at –40°C
3. Frostbite possible in 5 minutes at –48°C
4. Frostbite possible in 2 minutes or less at –55°C
Considering the risk of frostbite, W can be interpreted as follows:
1. Risk of frostbite in prolonged exposure (30 minutes) at –28°C
2. Frostbite possible in 10 minutes at –40°C
3. Frostbite possible in 5 minutes at –48°C
4. Frostbite possible in 2 minutes or less at –55°C
32.Required Clothing Insulation
Required clothing insulation — insulation required (IREQ) is an assessment method based on heat-balance equations.
It calculates the required thermal insulation of clothing in a given thermal environment and activity level.
The IREQ can be calculated for two levels of thermal strain: low strain (neutral IREQ) and high strain (minimal IREQ).
Required clothing insulation — insulation required (IREQ) is an assessment method based on heat-balance equations.
It calculates the required thermal insulation of clothing in a given thermal environment and activity level.
The IREQ can be calculated for two levels of thermal strain: low strain (neutral IREQ) and high strain (minimal IREQ).
33.If the thermal insulation of the clothing is not sufficient for given conditions, the IREQ equation can be used to calculate the duration-limited exposure time (DLE time), which expresses the allowable exposures time before reaching the threshold of low or high thermal strain.
It is important to note that the IREQ equation gives the required thermal insulation for the whole body, but the local cold strain — e.g., in hands, feet, and respiratory system — should always be evaluated separately.
It is important to note that the IREQ equation gives the required thermal insulation for the whole body, but the local cold strain — e.g., in hands, feet, and respiratory system — should always be evaluated separately.
33.Physiological Measurement
Physiological measurements of cold stress are based on measurements of superficial skin and body core temperatures and sometimes also heat loss.
The measured skin and deep-body temperatures are usually interpreted in five levels (comfort, discomfort, performance degradation, adverse health effects, and tolerance).
Physiological measurements of cold stress are based on measurements of superficial skin and body core temperatures and sometimes also heat loss.
The measured skin and deep-body temperatures are usually interpreted in five levels (comfort, discomfort, performance degradation, adverse health effects, and tolerance).
34.Thermal Sensation
The degree of thermal discomfort is recorded after the question "Do you find this…?” The classification is as follows: comfortable (0), slightly uncomfortable (1), uncomfortable (2), very uncomfortable (3), and extremely uncomfortable (4).
Scales for thermal preference and personal acceptability statement are also presented in ISO 10551 (1995).
35.Cold Strain Index
A recently developed cold strain index (CSI), based on core (Tcore) and mean skin temperatures (Tsk), iscapable of indicating cold strain in real time by analyzing existing databases. This index rates cold strainon a universal scale of 0 to 10.
36.Conductive Heat Loss
A recently developed ISO standard (ISO NP 13732, unpublished) quantifies the cold stress caused by conductive heat loss. It also gives time limits for contacting different materials in different temperatures.
37.Other Methods
Vocabulary and symbols (ISO DIS 13731, 2001)
• Principles and applications of relevant international standards (ISO 11399, 1995)
• Instruments and methods for measuring physical quantities (ISO 7726, 1998)
• Determination of metabolic heat production (ISO 8996, 1990)
• Medical supervision of individuals exposed to extreme hot or cold environments (ISO DIS 12894,2001)
The degree of thermal discomfort is recorded after the question "Do you find this…?” The classification is as follows: comfortable (0), slightly uncomfortable (1), uncomfortable (2), very uncomfortable (3), and extremely uncomfortable (4).
Scales for thermal preference and personal acceptability statement are also presented in ISO 10551 (1995).
35.Cold Strain Index
A recently developed cold strain index (CSI), based on core (Tcore) and mean skin temperatures (Tsk), iscapable of indicating cold strain in real time by analyzing existing databases. This index rates cold strainon a universal scale of 0 to 10.
36.Conductive Heat Loss
A recently developed ISO standard (ISO NP 13732, unpublished) quantifies the cold stress caused by conductive heat loss. It also gives time limits for contacting different materials in different temperatures.
37.Other Methods
Vocabulary and symbols (ISO DIS 13731, 2001)
• Principles and applications of relevant international standards (ISO 11399, 1995)
• Instruments and methods for measuring physical quantities (ISO 7726, 1998)
• Determination of metabolic heat production (ISO 8996, 1990)
• Medical supervision of individuals exposed to extreme hot or cold environments (ISO DIS 12894,2001)
38.Heat Stress Indices
39.Heat Stress Indices
40.Heat stress occurs when the body absorbs or produces more heat than can be dissipated through thermoregulatory processes, and illness and death can result from the increases in core temperature (Parsons, 1993).
Heat stress can occur in unique situations, such as firefighting.
Heat stress can occur in unique situations, such as firefighting.
41.Guidelines for Investigating Heat Stress
1. Review occupational injury logs/records for indications of heat stress problems.
2. Conduct employee/employer interviews to ascertain the nature of employee complaints, what and where the potential heat sources are, and what action has been taken to prevent heat stress problems.
3. Conduct a walk-around inspection of heat sources; perform temperature measurements; calculate relative heat load per employee; determine the need for engineering controls.
4. Determine the workload category of each job performed in hot conditions
1. Review occupational injury logs/records for indications of heat stress problems.
2. Conduct employee/employer interviews to ascertain the nature of employee complaints, what and where the potential heat sources are, and what action has been taken to prevent heat stress problems.
3. Conduct a walk-around inspection of heat sources; perform temperature measurements; calculate relative heat load per employee; determine the need for engineering controls.
4. Determine the workload category of each job performed in hot conditions
41.Heat Stress Indices: Body Measurement
The most direct measure of heat stress is to record the core temperature of the body. The most accurate instrument is a rectal thermometer, but often this is impractical in work situations. Ear or skin temperature measurements do not provide accurate and reliable estimates of core temperature.
The most direct measure of heat stress is to record the core temperature of the body. The most accurate instrument is a rectal thermometer, but often this is impractical in work situations. Ear or skin temperature measurements do not provide accurate and reliable estimates of core temperature.
42.Heat Stress Indices: Environmental Measurements
Environmental heat measurements should be made at, or as close as possible to, the specific work area where the worker is exposed. When a worker is not continuously exposed in a single hot area but moves between two or more areas having different levels of environmental heat, or when the environmental heat varies substantially at a single hot area, environmental heat exposures should be measured for each area and for each level of environmental heat to which employees are exposed.
Environmental heat measurements should be made at, or as close as possible to, the specific work area where the worker is exposed. When a worker is not continuously exposed in a single hot area but moves between two or more areas having different levels of environmental heat, or when the environmental heat varies substantially at a single hot area, environmental heat exposures should be measured for each area and for each level of environmental heat to which employees are exposed.
43.Heat Stress Indices
Wet-Bulb Globe Temperature Index
Heat Stress Index (HSI)
Index of Thermal Stress (ITS)
Required Sweat Rate (SWreq)
Wet-Bulb Globe Temperature Index
Heat Stress Index (HSI)
Index of Thermal Stress (ITS)
Required Sweat Rate (SWreq)
44.Wet-Bulb Globe Temperature Index
45.Heat Stress Index (HSI)
The heat stress index (HSI), formulated by Belding and Hatch (1955), compares the sweat evaporation required to maintain thermoneutrality (Ereq) with the maximum evaporation achievable in that setting (Emax) as follows:
The heat stress index (HSI), formulated by Belding and Hatch (1955), compares the sweat evaporation required to maintain thermoneutrality (Ereq) with the maximum evaporation achievable in that setting (Emax) as follows:
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