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
Comfort, cont.

• 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

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 bodys 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 3540 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.