Asp 09 - Ventilation & Thermal Stress

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ventilation protects worker health by removing airborne containation from worker's breathing zone

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2 ventilation method:

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1. local exhaust- remove contaminated air from breathing zone (ex. fume hood)

2. dilution- bring in bunch of clean air to reduce contamination concentration

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ventilation

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Q = VA

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ventilation assumptions for exam:

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1. assume standard temp and pressure

2. dry air

3. no significant changes in temp or pressure

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V1A1 = V2As

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conservation of air flow

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2 type of energy

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potential and kinetic

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energy is ventilation is pressure

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Front 8

kinetic energy is velocity pressure

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always positive

Front 9

potential energy is static

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can be neg or positive

Front 10

the force applied by moving air hitting a surface

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velocity pressure

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velocity pressure is always positive

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Front 12

the force exerted by air molecules striking a containers' surface

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static surface

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static pressure is same in all direction

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can be pos or neg

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Change in static pressure causes air to move

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Front 15

air moves from high static pressure to low static pressure

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Front 16

sum of static pressure and velocity pressur is?

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total pressure

Front 17

when air moves through ventilation system, total pressure decr.

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b/c resistance of hood, rough duct surface, particles on air cleaner, fan blowing air out.

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2 hood category

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external hood and enclosing hood. enclosing is more effective

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external hoods

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1. duct opening

2. slot hood

3. compoud hood

4. receiving hood- canapy or abrasing grinding wheel (momentum of an abrasive grinding wheel help push air)

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enclosing hoods

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- lab hoods, clove boxes

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hood design criterials

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- cross drafts

- capture velocity: toxicity, particulate or vapor contamination inertia

- work position

- hood efficiency

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best hood design:

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-enclose work process entirely

- remove only the sides to allow process to work

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capture velocity

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the min hood-induced air velocity necessary to capture and convey the contaminant into the hood

Front 24

capture velocity is based on generation velocity, cross-drafts, toxicity, and hood face area

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Front 25

hood energy loss: energy is converted from potential energy (static pressure) to kinetic energy (kinetic energ) at the hood

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Front 26

Dilution Ventilation Principles: choose dilution ventilation control only if all conditions are met:

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- no workers exposed to excessive concentrations

- local exhaust not feasible or inappropriate

- contaminant is not highly toxic

- contaminant is easility transported to exhaust point

- costs of supply are air not excessive

- existing ventilations rates are relatively low

Front 27

don't use highly toxic chemical with dilutions ventilations bc ventilation system might die.

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Front 28

consider these when designing a dilution ventilation syst:

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- local exhaust opening near comtamination

- workers should be positioned btw supply and contaminant

- replace exhausted air

- outside contaminants should be considered when placing locations of air intake

- consider mixing effects of room configuration

Front 29

metabolic heat

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energy generated while the body is being active; measured in kcal/hr

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Convention

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the transfer of heat directly to object...

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radiation

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the transfer of heat through infrared radiation

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Evaporation

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the transfer of heat to the environment through evaporative cooling

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Wet bulb globe temp

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estimate of environ contribution to heat stress

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WBGT (solar) vs (nonsolar)

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outside vs inside

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Psychrometric chart

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provides a graphical relationship of water vapor pressure, dry bulb temp, wet bulb temp, relative humidity, and dewpoint

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Heat illness

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Heat...

- stroke

- hyperpyrexia

- syncope

- exhaustion

- cramps

- rash

- fatigue

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heat stroke

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- body fails to regulate body temp

- skin is hot and dry

- confused behavior

- loss of consciousness

- convoltion

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heat hyperpyrexia

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less severe form of heat stroke

- some sweating still occurs

- other symptoms are less severe

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heat syncope

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- non-acclimatized persons standing in the heat faint

- blood flow reduced to the brain

- treatment: remove victim to cooler location and lie down

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heat exhaustion

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- excessive loss of water through sweating

- fatigue

- nausea

- headache or giddiness

- cold, clammy skin

- diluted pupils, heavy prespiration,

- treatment: get to cooler location, replace body fluid

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heat cramps

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- painful muscle cramps during or following work in hot environment

- body salts loss through sweat

- weak, lightheaded, heavy pespiration

containin- treatment: replace fluids with

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heat rash

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- small blishter eruptions during heat exposure

- treatment: keep skin clean and dry

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heat fatigue

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- reduced performance from workers

- take frequent breakds

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heat illness prevention

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- drink water

- take frequent breaks

- PPE: cooling vest

- engineering controls: AC, mists in air, fans moving air (not good if just blowing hot air)

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heat illness monitoring

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- excessive strain is probably when these occurs:

-- sustained heart rate = 180 bpm - age (minus age)

--- recovery heart rate (after 1min) > 120 bpm

-- core bod temp > 101.3 F (38.5 C)

-- sudden and severe sympt: fatigue, nausea, dizziness, lightheadedness

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cold illness

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- body shivering to warm up

- trench foot

- chillblains

- cold urticaria

- frostbite

- hypothermia

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trench foot

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- several days of exposure to cold (not freezing) temp and moist skiin

- vascoconstriction in feet and leg

- pale appearance and numbness

_ looks like under water for long time, wrinkle

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chilblains

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- itchness, painful redness of skin (end of toes)

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cold urticaria (hives

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- cold can cause histamines release in tissue

- produce itchy red blotches

- only occur in some people

- vomitting, ...

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frostbite

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- freezing of body tissue

- white or grayish yellow skin

- damage dependent on depth of freezing

- treatment: warmign slowly

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hypothermia

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- general lowing of core body temp

- shivering initially occurs

- numbness

- disorientation

- confusion

- amnesia

- impaired judgement

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core body temp

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26-35 C

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hypothermia

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- unconsciousness

- cardiac arrhythmia

- muscular ridgdity

- ventricular fibrillation

- respiratory arrest

- death

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wind chill factors/ chart

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cold illness prevention

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- provide heat source where feasible

- minimize exposure time

- protective clothing

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password

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swimming