Climate

1. Climate • Air volume and quality • amount • contaminants • ventilation • Comfort • Stress • Heat stress • Cold stress

2. Air Volume and Quality • Volume of air required is proportional to local contaminants. • Usually not a problem in office buildings, but … • Carbon dioxide may be limiting. • Body odors and cigarette smoke can be contaminants. • Danger of ‘sick building syndrome’ • For forced-air heating and cooling, ventilation volume may be determined by room temperature.

3. Shop Environments • Local contaminants may pollute the air. • Solution strategies: • Decrease the concentration of the contaminant. • Reduce worker exposure duration. • Consider ventilation. • Area ventilation • Use when contaminant sources are diffuse. • Keep the contaminant source downwind from the person. • Locate the source as close to the exhaust as possible.

4. Shop Environments, cont. • Local ventilation • Capture the contaminant directly. • Dump exhaust air outdoors or filter it. • Make filter systems fail-safe. • For explosive substances, TLV is limiting. • Consider reusing the air after filtration. • Clean rooms • Provide clean air. • Minimize contamination • personnel • materials

5. Comfort • Factors • Dry bulb temperature • Water vapor pressure • Air velocity • Radiant temperature • Metabolic rate • Clothing • Time of exposure

6. For standard conditions Use psychrometric chart to find comfort zone (fig. 25.1, pg. 490.) Use percentage of people dissatisfied (PPD) calculation. Adjustments for nonstandard conditions Clothing Activity Air velocity Mean radiant temperature Time of exposure Time of day and season of year Gender and age of occupant Comfort, cont.

7. Individual Adjustment • Conventional approach is to set conditions to match comfort zone. • Desktop controls allow individuals to set their own conditions. • Occupancy sensors turn off equipment. • Energy savings may be substantial.

8. Heat Stress • Effects on performance and health • Performance deteriorates well before physiological limits are reached. • Illnesses include heat stroke, heat exhaustion, heat cramps, and heat disorders. • For health, use heart rate, blood pressure, or body temperature criteria. • Design using comfort as the criterion. • Setting environmental limits • Measure physiological responses during work • Predict the stress beforehand based on predicted environments and tasks • WBGT combines effects of the four environmental comfort factors.

9. Reduction of Heat Stress • Heat balance equation: S = M – (±W) + (±R) + (±C) + (±E) + (±K) • Consider human body heat storage. • Reduce metabolic rate. • Consider work being done. • Reduce radiant load. • Maximize convective heat loss. • Increase evaporative heat transfer. • Consider conductive cooling.

10. Heat Transfer • Radiant • Driving force is difference between the 2 temperatures, each to the 4th power. • Reduce radiant load by working in the shade. • Use clothing (hats and long-sleeved shirts). • Use a heat shield with ovens, welding, and molten glass. • Convective • Driving force is the difference between the temperatures. • Keep temperature of the environment below 35ºC (95ºF.) • Increase air velocity on the skin. • Permit air circulation around clothing. • Humid moving air can cool a worker by convection.

11. Heat Transfer, cont. • Evaporative • Sweating capacity increases with acclimatization. • Prevent dehydration by replacing water. • Evaporation can be limited by humidity. • Reduce effect of humidity by increasing air velocity or decreasing water vapor pressure. • Non-permeable clothing prevents sweat from evaporating.

12. Cold Stress • Cold causes discomfort, reduced mental performance and dexterity, pain, loss of extremities, and death. • Hand skin temperature critically affects dexterity and tactile sensitivity. • Vigilance decreases when the core temperature drops. • Environmental Limits • Wind chill index combines all factors for cold. • Wind chill is based on cooling water, not a clothed living human. • Use wind chill for livestock and for a crude index for precautions.

13. Cold Stress, cont. • Protection • Layer clothing. • Shoes should accommodate two pairs of socks. • Keep clothing dry. • Protect the head. • Warm the hands by wearing a jacket. • For exercise, use breathable fabrics. • Reduce air velocity. • Other Factors in Cold Stress • Cover vents or use diffusers or deflectors. • Keep floor temperature at 23ºC (73.5ºF) in offices. • Avoid contact with cold metal. • Drink fluids to prevent dehydration. • Avoid caffeine (a vasodilator.)

14. Toxicology • Deals with long-term effects of foreign chemicals on the body. • Chemicals affect the body with doses producing a response. • Controls can be engineered, administration, or personal protection.

15. Effects of Poisons • Effects may be permanent or reversible. • Threshold limit values are based on nonreversible functional changes in an organ. • Response may lag the dose by many years. • Workers tend to ignore hazards with long delayed response times. • Financial benefits accrue to organizations, heath costs to individuals. • Teratogens cause defects in fetal development. • TLV approach considers humans to be the most sensitive species.

16. Dose/Response • Chemicals can be detected in extremely low concentrations. • The problem is to define “excess.” • Poisoning depends on the rate of input, kind of poison, body size, target organ susceptibility, and poison removal capability. The Leaky Bucket

17. Poison Routes • To enter the body, a poison must enter the blood. • Poisons may be characterized by their ability to penetrate the body’s perimeter. • The most important entrance points are the skin, mouth, and lungs.

18. Skin • The skin is a superb barrier. • Most compounds run off the skin rather than penetrate. • Problems arise from wet clothing and cuts and abrasions. • In general poisons that enter through the skin are not serious problems.

19. Dermatitis • Accounts for 35–40% of reported industrial disease. • Causes include: • Mechanical and physical • Chemical • Plant poisons • Biological agents

20. Dermatitis Prevention • Protective clothing • Good housekeeping around workstations • Barrier creams • Personal cleanliness • Cleanliness of clothing

21. Mouth • For adults the problem is toxic compounds in food or drink. • Forbid eating, drinking, and smoking in work areas. • Provide clean, convenient areas for eating and drinking. • Consider enclosing these areas.

22. Lungs • The lungs are the major route in poison absorption. • Particle size is the most important characteristic in inhalation. • Particles below 10 μm in diameter tend to be retained in the lungs. • Straight and short fibers penetrate deeper than long or curved ones.

23. Interior Poison Targets • Respiratory system • Blood • Other organs • Fetuses

24. Poison Elimination • The liver biotransforms compounds. • Transformed materials leave the liver in bile for excretion. • Blood from liver goes to kidneys and general circulation. • Kidney puts transformed compound into urine. • Not all blood goes to liver and not all of compound is transformed.

25. Threshold Limit Values • Issued by American Conference of Governmental Industrial Hygienists. • Three different types: • Time-weighted average (TLV-TWA): • recognizes chronic effects • Short-term exposure limit (TLV-STEL): • concerned with acute effects • Ceiling (TLV-C): an absolute limit of concentration • Applying TLVs • Excursions are permitted above the TWA and STEL but not the ceiling. • TLVs assume concentration × time = a constant, which is unlikely. • STEL limits duration of high exposures. • TLVs are based on 8-h exposure

26. Example of TLV Calculation • Assume worker exposed to acetone for 4 h at 500 ppm, 2 h at 750 ppm, 2 h at 1500 ppm. TWA = [500 × 4 + 750 × 2 + 1500 × 2] ÷ 8 = 812 • Is this acceptable?

27. Controlling Exposure • Engineering Controls: • Substitute a less harmful material. • Change the material or process. • Enclose (isolate) the process. • Use wet methods. • Provide local or general ventilation. • Use good housekeeping. • Control waste disposal.

28. Controlling Exposure, cont. • Personal Protective Equipment • This is the last line of defense. • Use equipment that fits properly. • Maintain the equipment and know how to use it. • Know its limits. • Have clothing cleaned professionally. • Have workers shower before leaving work. • Administrative controls: • Screen potential employees. • Periodically examine employees. • Train engineers, supervisors, and workers. • Reduce exposure time.