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Introduction to Industrial Hygiene


The Original Metallica. Georgius Agricola published a 12 volume set in 1556, De Re Metallica ... Metallica Quotes ' ... Metallica cont. ... – PowerPoint PPT presentation

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Title: Introduction to Industrial Hygiene

Introduction to Industrial Hygiene
  • Safety Management
  • TM 650
  • Carter J. Kerk
  • Industrial Engineering Department
  • South Dakota School of Mines
  • Summer 2007

Introduction to Industrial Hygiene
  • Read Asfahl
  • Chapter 9, Health and Toxic Substances
  • Chapter 10, Environmental Control and Noise

Industrial Hygiene
  • Part science, part art
  • Industrial Hygiene is the application of
    scientific principles in the workplace to prevent
    the development of occupational disease or injury
  • Requires knowledge of chemistry, physics,
    anatomy, physiology, mathematics

IH Topics
  • Toxicology
  • Occupational Health Standards
  • Airborne Hazards
  • Indoor Air Quality
  • Skin Disorders
  • Noise Exposure
  • Radiation
  • Thermal Stress
  • Anatomy
  • Biohazards
  • Chemicals
  • Illumination
  • Personal Protective Equipment
  • Ventilation
  • Vibration
  • Sampling

History of IH
  • Disease resulting from exposure to chemicals or
    physical agents have existed ever since people
    chose to use or handle materials with toxic
  • In the far past, causes were not always recognized

Earliest Recordings
  • Lead poisoning among miners by Hippocrates, 4th
    century BC
  • Zinc and sulfur hazards by Pliny the Elder, 3rd
    century BC

The Original Metallica
  • Georgius Agricola published a 12 volume set in
    1556, De Re Metallica
  • Town physician in Saxony
  • Silver mining
  • Described diseases of lungs, joints, eyes
  • Woodcuts (see next slides)

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Metallica Quotes
  • If the dust has corrosive qualities, it eats
    away at the lungs, and implants consumption in
    the body
  • Later determined to be silicosis, tuberculosis,
    and lung cancer

Metallica Quotes
  • there is found in the mines black pompholyz,
    which eats wounds and ulcers to the bone this
    also corrodes iron . . . There is a certain kind
    of cadmia which eats away at the feet of workmen
    when they have become wet, and similarly their
    hands, and injures their lungs and eyes.
  • Later recognized as manifestations of toxicity of
    arsenic and cadmium

Metallica cont.
  • A young American named Herbert C. Hoover and his
    wife, L.H. Hoover, translated Agricolas work
    into English.
  • The translation was published in 1912
  • Hoover graduated from Stanford in 1891 as a
    Mining Engineer
  • Hoover served as the 31st president of the US
    (1929 1933)

  • Published work describing mercury poisoning of
    miners in 1567
  • His famous quote, All substances are poisons
    there is none which is not a poison. The right
    dose differentiates a poison and a remedy.
  • This provided the basis for the concept of the
    dose-response relationship.

Dose-Response Relationship
  • The toxicity of a substance depends not only on
    its toxic properties, but also on the amount of
    exposure, or the dose
  • Paracelsus differentiated between
  • Chronic (low-level, long-term) poisoning
  • Acute (high-level, short-term) poisoning

Bernardino Ramazzini (1633-1714)
  • Wrote a book, De Morbis Artificum (Diseases of
    Workers), starting the field of occupational
  • Urged physicians to ask the question, Of what
    trade are you?
  • He described diseases associated with various
    lower-class trades, such as corpse carriers and

Other Pioneers around 1770
  • Sir George Baker
  • Linked Devonshire colic to lead in cider
  • Percival Pott
  • Linked soot exposure and scrotal cancer in
    chimney sweeps

The Mad Hatter
  • Lewis Carrolls Alice in Wonderland (1865)
  • Mad Hatter exhibited symptoms of mercury
    poisoning, such as mental and personality changes
    marked by depression and tendency to withdraw
  • Mercury was used in processing hides made into
  • Bars were installed on windows at hat factories
    presumably to prevent afflicted workers from
    leaping during bouts of depression

Protection Starts to Arrive
  • English Factory Act, 1833, allows injured workers
    to receive compensation
  • English Factory Inspectorate, 1878
  • US Workers Compensation started in 1908-1915 in
    several states (state programs, not federal)
  • Occupational Safety Health Act enacted in 1970
    creating OSH Administration
  • Created regulations, inspections, recordkeeping,
    enforcement, etc.

Birth of Industrial Hygiene
  • A few industrial hygienists were practicing in
    early 1900s
  • Physicians sometimes saw the industrial hygienist
    as a threat to their realm of expertise
  • Dr. Alice Hamilton was a pioneer Occupational
    Physician and female pioneer. She helped foster
    the field of IH in the US
  • American Industrial Hygiene Association (AIHA)
    formed in 1939

Industrial Hygiene
  • Other terms
  • Occupational Hygiene
  • Environmental Hygiene
  • Environmental Health

Professional Organizations
  • American Industrial Hygiene Association (AIHA),, member organization
  • American Conference of Governmental Industrial
    Hygienists (ACGIH),, member
    organization for government employees
  • American Board of Industrial Hygiene (ABIH),, independent organization that
    administers certification programs for industrial
    hygiene professionals
  • IHIT, Industrial Hygienist in Training
  • CIH, Certified Industrial Hygienist
  • Requires maintenance of certification

Scope of IH
  • Recognition, Evaluation, and Control of hazards
    or agents
  • Chemical Agents
  • Dusts, mists, fumes, vapors, gases
  • Physical Agents
  • Ionizing and nonionizing radiation, noise,
    vibration, and temperature extremes
  • Biological Agents
  • Insects, molds, yeasts, fungi, bacteria, viruses
  • Ergonomic Agents
  • Monotony, fatigue, repetitive motion

Control of Agents
  • Controls in this order of preference
  • Engineering Controls
  • Engineering changes in design, equipment,
  • Substituting a non-hazardous material
  • Administrative Controls
  • Reduce the human exposure by changes in
    procedures, work-area access restrictions, worker
  • Personal Protective Equipment / Clothing
  • Ear plugs / muffs, safety glasses / goggles,
    respirators, gloves, clothing, hard-hats

1. Recognition of health hazards
  • Walk-through survey with someone knowledgeable of
    the processes
  • Regular intervals, keep records
  • Planning stage reviews
  • Modification reviews
  • MSDS reviews

2. Evaluation of hazards
  • Measurements
  • Air sampling, noise meters, light meters, thermal
    stress meters, accelerometers (vibration)
  • Calculation of dose
  • Level and duration of exposure
  • Keep records

3. Control of Hazards (Prioritized)
  • 1 Engineering
  • Substitute a less hazardous material, local
    exhaust ventilation
  • 2 Administrative
  • Worker rotation, training
  • 3 Personal Protective Equipment
  • Respirators, gloves, eye protection, ear
    protection, etc.

4. Recordkeeping
  • Important in all phases of the program
  • Often required by regulation
  • 29 CFR 1904
  • Increase program effectiveness
  • Useful in legal challenges

5. Employee training
  • Effective component if total program is
    implemented and engineering controls are first
  • Often required by regulation
  • Right to Know or Hazard Communication Standard
    29 CFR 1910.1200
  • Regular intervals
  • Keep it interesting and effective, use a variety
    of techniques
  • Keep records of dates, individuals, topics,

6. Program review
  • Regular intervals (yearly, semi-annual)
  • Review the written program as well as the
  • Updates for new regulations, new chemicals, new
    processes, or any changes
  • Audit components of the program
  • Internal OSHA inspection
  • Involve employees, consultants, management


  • Toxicity The ability of a substance to cause
    harm or adversely affect an organism
  • Toxicology The science and study of harmful
    chemical interactions on living tissue

Occupational Toxicology
  • Workplace exposure to chemicals
  • You or someone you know has probably experienced
    an episode of toxicology
  • Injury or death due to
  • Smoke inhalation
  • Confined space incident
  • Ingestion or absorption of a chemical

The Dose-Response Relationship
  • A time of exposure (dose) to a chemical, drug, or
    toxic substance, will cause an effect (response)
    on the exposed organism
  • If the amount or intensity of the dose increases,
    there will be a proportional increase in the

  • Dose The amount of a substance administered (or
    absorbed), usually expressed in milligrams of
    substance per kilogram of the exposed organism
  • Response The effect(s) of a substance may be
    positive or negative

Dose Response Curve
Acute and Chronic Terminology Exposure as well
as Response
  • Acute exposure short time / high concentration
  • Chronic exposure long-term, low concentration
  • Acute response rash, watering eyes, cough from
    brief exposure to ammonia
  • Chronic response emphysema from years of
    cigarette smoking

Possible Response Levels
  • No response at low dosage levels there may be
    no response at all
  • Threshold dose the lowest level of dosage at
    which a response is manifested
  • NOAEL no observed adverse effect level
  • NEL no effect level
  • Above threshold dose response can be positive
    up to a point and then could become toxic to the
  • Different people or organisms will exhibit a
    variety of responses

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Indicators of Relative Toxicity
  • Toxicity ability of a substance to cause harm or
    have an adverse affect
  • How much harm?
  • What aspect of the population?
  • Notation
  • LD, lethal dose
  • LC, lethal concentration
  • ED, effective dose
  • EC, effective concentration

LD50 a measure of relative toxicity
  • Most common toxicity notation
  • Determined in the lab and based on an acute
    exposure to adult test animal
  • Lethal dose that produces death in 50 of the
    exposed population
  • LD50, 35 mg/kg, oral, rat
  • 35 mg of dose per kg of rats body weight, when
    administered orally, produces death in 50 of
    exposed population
  • Comparing the LD50 between two substances gives
    the relative toxicity between the two substances

LD50 Relative Toxicity
Effect of route of administration
How can we interpret animal test?
  • Animal tests can give an indication of relative
    toxicity which can be extrapolated to humans
  • Problems
  • Toxicity variance between organisms
  • Animal doses (strength or time) may be higher
    than realistic human exposures
  • On a body weight basis, humans are usually more
    susceptible to toxic effects, sometimes by a
    factor of ten
  • Therefore, human interpretation requires use of a
    safety factor

Epidemiological Studies
  • Prospective epidemiological study
  • Take a cohort (or group of individuals) with a
    common exposure
  • Follow through time to see if they develop
  • Retrospective epidemiological study
  • Take a cohort with a disease and trace back
    through time to see if there is a common exposure
  • These are difficult with many confounding
    factors, but are quite valuable

Latency Period
  • Long delay between exposure and disease
  • Some diseases may not develop for many years
  • Lung cancer may occur as much as 30 years after
    exposure to asbestos
  • This makes animal studies and epidemiological
    studies even more difficult, but also very

Routes of Exposure
  • Inhalation
  • Ingestion
  • Absorption through the skin
  • Less common
  • Injection
  • Absorption through eyes and ear canals

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  • Most common route of entry into body
  • Therefore our area of highest concern
  • Lungs are designed for efficient gas exchange
    between the air and bloodstream
  • Lungs have up to 1000 square feet of exchange
    area (about 32 feet by 32 feet)
  • Normal days breathing volume 8 cu ft
  • Therefore great potential for toxins to enter

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Skin Absorption (2nd most important route)
  • Skin surface area is about 20 square feet (4.5 ft
    by 4.5 ft)
  • Compare to 1000 sq ft for lungs
  • Materials can be absorbed into blood stream just
    below the skin surface or toxins can be stored in
    fat deposits
  • Obviously workers can easily expose their hands
    into solvents, oils, chemicals, etc., plus these
    materials can be sprayed or rubbed on other parts
    of the body
  • Many chemicals are either soluble in water or in
    oil (fat, lipid)
  • The skin easily absorbs lipid-soluble materials
  • Solvents
  • Water-soluble materials are not easily absorbed
  • Lipid layer on skin provides a barrier

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Ingestion (3rd most important route)
  • Ingestion is not usually intentional
  • Unintentional ingestion
  • Failure to wash hands and face before meals
  • Eating/drinking in areas where airborne hazards
  • Lighting cigarettes with dirty hands
  • Application of cosmetics
  • Use of chewing tobacco or gum in contaminated

  • The digestive tract is moist and designed for
    efficient absorption
  • Surface area of intestines is greatly increased
    by small projections (villi)
  • Thin surfaces, highly vascularized
  • Materials easily transferred to bloodstream

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  • Less common
  • Possible hazards
  • Outdoor work, construction sites, hazardous waste
    sites, plants, animals, reptiles, insects,
    abrasions, puncture wounds, cuts

Absorption into eyes and ears
  • Much less common but possible
  • Moist surfaces

Distribution of Toxins
  • Once toxins are in the body, there are several
    mechanism of movement and action
  • Inhalation
  • Toxics may enter bloodstream
  • Toxics may irritate or scar lung tissues directly
  • Skin Absorption
  • Toxics may enter bloodstream
  • Toxics may irritate, corrode or burn skin directly

Once absorbed into the body, toxins can move to
other tissues and organs through various ways
  • Filtration
  • Toxins move through membrane pores
  • Diffusion
  • Movement from higher concentration to lower
  • Active transport
  • Movement across a membrane otherwise impermeable
    by a transport mechanism
  • Chemical reaction or carrier molecule, requires
  • Phagocytosis
  • Toxins eat or engulf other cells or by use of
    white blood cells

  • Important in metabolism, energy storage, protein
  • Receives blood from digestive tract and works to
    concentrate, transform, and excrete substance
    (both good and bad toxins)
  • Thus produces bile (enriched) which is returned
    to the intestines

  • Receive 25 of cardiac output for filtration
  • Primarily for elimination of water soluble
  • Large molecules (proteins) and lipid soluble
    materials are reabsorbed through the tubules of
    the nephron
  • Nephron functional unit of the kidney (see next
  • Materials pass by filtration, diffusion, active

Classes of Toxins and Toxic Responses
  • Irritants and Sensitizers
  • Systemic Toxins
  • Neurotoxins
  • Reproductive Toxins
  • Carcinogens

Occupational Health Standards

Exposure Limits
  • Mainly concerned with air quality values in the
  • Air concentration below which health hazards are
    unlikely to occur among most exposed workers
  • Based on scientific studies (animal, human)
  • Other topics noise, electromagnetic fields,
    ionizing radiation, etc.

Sources of Exposure Limits
  • OSHA limits are the only ones enforceable as law
  • Other sources
  • ANSI (American National Standards Institute)
  • ASTM (American Society for Testing Materials)
  • AIHA

Exposure Limit Terms
  • TWA Time-Weighted Average
  • 8 hour, 15 minute, 5 minute, instantaneous
  • 8-Hr TWA (CxTx)(CnTn)/8
  • Cx concentration measured during time interval
  • n total number of intervals measured
  • Make sure time intervals in numerator match time
    in the denominator
  • Concentrations
  • Parts per million (ppm) gases, vapors
  • Milligrams per cubic meter (mg/m3) solids
    (fumes, dusts, mists)

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  • OSHA PELs are found in Tables Z-1 and Z-2 of
    29CFR1910 Subpart Z
  • Use these to look up substance-specific standards

Example PELs (Table Z-1)
Notes PELs are 8-hr TWA unless otherwise noted.
C refers to ceiling limit
Example Benzene PEL
  • Table Z-2
  • 8-hr TWA 10 ppm
  • Acceptable ceiling concentration 25 ppm
  • Acceptable max peak above acceptable ceiling
    concentration for an 8-hr shift 50 ppm for 10
  • See 29CFR1910.1028 for more specific standards on

  • Substances known to cause cancer
  • NIOSH uses notation Ca
  • OSHA addresses carcinogens through
    substance-specific regulations
  • ACGIH uses a 5 category system
  • A1 through A5

Respiratory Protection Standard
  • 29 CFR 1910.134
  • Assign responsibility for program
  • Written procedures on selection, use and care of
  • Medical surveillance program
  • Employee training on use, care and limitations of
  • Fit testing appropriate for contaminants

Respiratory Std Cont.
  • Procedures for cleaning, storing, maintaining,
    and inspecting respirators
  • Periodic monitoring of contaminant levels
  • Periodic review of the program for effectiveness

  • Hazardous Waste Operations and Emergency Response
  • 29 CFR 1910.120 (1926.69 Construction)
  • Ensure health and safety of workers at sites
    where hazardous materials have been either
    accidentally released or dumped or where they are
    treated, stored, or disposed of.

Confined Space Standard
  • 29 CFR 1910.146
  • Confined Space
  • Large enough to enter and perform work
  • Limited or restricted means for entry or exit
  • Not designed for human occupancy
  • Permits

Occupational Noise Exposure Standard
  • 29 CFR 1910.95

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Airborne Hazards

  • Route of entry Airborne hazards are the most
    serious concern
  • Processes welding, grinding, spraying, hot
    processes, engine exhausts
  • Pollen, spores
  • Lungs efficient transfer of gases in and out of
    the body
  • But also provide a route of entry for hazards

Anatomy Function of the Lungs
  • Regions of the respiratory tract
  • Upper (nasopharyngeal)
  • Middle (tracheobronchial)
  • Lower (distal)

Upper (Nasopharyngeal)
  • Head, nose, nasal passages, sinuses, mouth,
    tonsils, epiglottis, back of throat
  • Lined with mucous membrane
  • Moist, sticky substance captures materials
  • Many small hairs
  • Help to trap particles

Middle (Tracheobronchial)
  • Trachea (windpipe), bronchi
  • Rings of cartilage and muscle
  • Cartilage provides structural support
  • Muscles contract to help force air
  • Coughing, sneezing
  • Lined with mucous membrane and hairs (cilia)
  • Cilia move like waves to push mucus and particles
  • Cigarette smoking can paralyze the cilia
  • Particle-laden mucus is removed by coughing,
    expectorating, or swallowing

Lower (Distal)
  • Bronchi split (bifurcate) repeatedly into two
    smaller passages (17 times) called bronchioles
  • Diameters decrease accordingly
  • Bronchioles end in microscopic sacs called
    alveoli (site of gas exchange)
  • Alveolar membrane is one cell thick
    (pneumocytes), surrounded by capillaries
  • Passive diffusion

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Microns (Micrometer)
  • One thousandth of a millimeter
  • 0.001 mm 1 mm
  • Greek letter, m
  • Useful in discussion of the size of inhaled
  • Visible to human eye
  • 100 mm 0.1 mm 0.01 cm
  • Human hair diameter
  • 5 500 mm 0.005 0.5 mm

Protective Mechanisms of the Respiratory Tract
  • Larger particles (10 mm)
  • Removed in nose and upper airways
  • 5 10 mm
  • Captured in tracheal region
  • 3 5 mm
  • Contact mucus lining in tracheal or bronchi
  • 0.5 3 mm
  • Can reach alveolar region, but few do

Capture of particles
  • Mucus (moist, sticky) linings
  • Tortuous pathway
  • Multitude of branches and splits
  • Large surface area of the route
  • Once particles are captured in mucus, they are
    removed by the mucociliary elevator or ladder
  • Cough reflex

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Protection in the Alveolar Region
  • Primary defense macrophages (specialized white
    blood cells)
  • Engulf foreign objects and attempt to dissolve
  • The smallest of particles may pass through cell
    membranes and lodge between cells (interstitial

Airborne Hazardous Materials
  • Aerodynamic Diameter
  • Useful for comparing particles with irregular
    shapes (dusts, fibers, etc.) to particles with
    regular shapes (droplets, mists, etc.)
  • The diameter of a reference spherical particle
    with a unit density of one (1) that has the same
    settling velocity as the contaminant particle

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Classes of Airborne Materials
  • Particulates / aerosols
  • Solid particles, dusts, fibers, mists, droplets,
  • Gases / vapors
  • Gaseous contaminants, vapors
  • Oxygen-deficient atmospheres
  • Combination
  • Any combination of particulates and/or gases,
    including oxygen-deficient atmospheres

Effects of Inhaled Materials
  • Airborne toxins
  • Local effects on tissues
  • Ammonia irritation in respiratory tract
  • Systemic effects through blood transport
  • Carbon tetrachloride (liver)
  • Solubility
  • More soluble upper respiratory tract, moist
    tissue around eyes ammonia
  • Less soluble penetrate to middle and lower
    respiratory tract phosgene gas

Occupational Diseases Associated with Airborne
  • Pneumoconiosis
  • Physiological Responses
  • Mineral Fibers and Other Fibers
  • Metals
  • Organic Particles

Indoor Air Quality

IAQ Outline
  • Introduction
  • Indoor air quality as a public health concern
  • Heating, ventilating, and air conditioning
    systems (HVAC)
  • Basic instruments for use in IAQ studies
  • Microorganism contamination and IAQ
  • Radon and asbestos

  • Indoor Air Quality (IAQ)
  • Recent phenomenon
  • Due to construction of energy conservation
    construction techniques starting in the 1970s
  • Sick Building Syndrome
  • Tight Building Syndrome
  • Gases emitted from cleaning chemicals, building
    materials, office furniture, carpets
  • Radon, asbestos, Legionella (put Rapid on the
    national map!)
  • Industrial and Non-Industrial (e.g., schools)
  • Ventilation Issues

Indoor Air Quality as a Public Health Concern
  • The energy crisis in the 1970s spawned
    construction of thousands of energy efficient
  • Sealed windows
  • Thermostats not accessible or adjustable by
  • Self-contained environments with controls for
    temperature, humidity, airflow
  • Complaints odors, too hot, too cold
  • Physical symptoms headaches, respiratory

  • Too hot, too cold, too drafty
  • Conditions vary with seasonal changes and HVAC

  • Air is too dry
  • Contributing to irritation of the respiratory
    tract and eyes
  • Too much humidity
  • Contributes to growth of microorganisms,
    encourages odors and mustiness

Stuffiness or Lack of Circulation
  • Can be related to location of diffusers or
    outlets relative to occupants
  • HVAC system is undersized, poorly maintained, or
    improperly operated
  • Poor circulation can lead to stratification of
  • Some areas benefit, other areas suffer
  • Dead zones may allow odors and CO2 to accumulate
    to unacceptable levels

  • Many objectionable odors coffee, body odor,
    vehicle exhaust, chemical smells
  • New construction or renovation odors fresh
    paint, off gassing from furniture or carpet
    fabric (formaldehyde)
  • Odors may be drawn in from outside
  • Air intakes located near loading docks, trash
    dumpsters, incinerators, exhaust stacks

Physical Symptoms
  • Dryness of eyes and respiratory tract, headaches,
    tiredness, upset stomach, runny nose, nasal
    congestion, drowsiness
  • CO2 levels 1000 ppm may cause headaches and
  • Symptoms are often non-specific enough to draw a
    cause-effect relationship

US Statistics on IAQ
  • About half of IAQ problems were attributed to the
    HVAC system
  • Poor system design
  • Poor maintenance
  • About 40 due to chemical contaminants or
  • In 10 of the cases, no cause could be found

Psychosocial Factors
  • Do not disregard this category
  • Job satisfaction, degree of control over ones
    environment, window placement and window control

OSHA Standards for IAQ
  • On December 17, 2001, OSHA withdrew its IAQ
    proposal and terminated rulemaking proceedings
  • Proposed
  • CO2
  • RH
  • Maintain HVAC records on original design
    specifications, cleaning, repairs
  • Exhausting designated smoking area to the outside
    and keeping them under negative pressure
  • Locating air intakes of systems to prevent
    capturing outside air contaminants

  • American Society of Heating, Refrigerating, and
    Air-Conditioning Engineers
  • 62-1989, Ventilation for Acceptable Air Quality
  • 55-1992, Thermal Environmental Conditions for
    Human Occupancy
  • 52-1992, Methods of Testing Air Cleaning Devices
    Used in General Ventilation for Removing
    Particulate Matter

Fresh Air Recommendations
  • ASHRAE Recommendations
  • 1905 30 cfm / person
  • 1936 10 cfm / person
  • 1973 5 cfm / person
  • Energy crisis concerns
  • 1989 20 cfm / person
  • Concerns about 2nd hand smoke

Basic Instruments for IAQ Studies
  • Thermometer
  • Velometer (air velocity)
  • Rotating vane anemometer
  • Heated-wire anemometer
  • Gas Detection Instruments
  • Detector tubes
  • Psychrometer (relative humidity)
  • Smoke tubes
  • IAQ multi-function instruments
  • Air temperature, humidity, CO2, air velocity,
    dewpoint, computer interface

Occupational Noise Exposure

Outline Occupational Noise Exposure
  • Physics of sound
  • Anatomy of the ear
  • Evaluating hearing ability and hearing loss
  • Standards for occupational noise exposure
  • Measuring noise in the occupational setting
  • Controlling noise

  • High levels of noise cause hearing loss
  • Hearing loss is mostly irreversible and usually
  • Noise can also produce stress, reduce
    productivity, and cause communication problems

Physics of Sound
  • Noise unwanted sound
  • Energy in the form of pressure waves
  • Waves can be described by frequency (f), speed
    (c), and wavelength (?)
  • c f ?
  • Sound moves at 344 m/sec in air, 6100 m/sec in
  • Some materials will amplify or reflect sound
  • Frequency (f) is related to pitch
  • Healthy, young person can detect 20 to 20,000 Hz
  • This declines with age and exposure history

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Sound Pressure Level
  • We can measure sound pressure
  • Force per unit area
  • SI units, pascal, Pa
  • All sound pressures are related to a reference
    sound pressure of 20 ?Pa (approximate lower
    threshold for human hearing at 1000 Hz)
  • Lp 20 log10 (P / 20 ?Pa)
  • Where Lp is the sound pressure, in decibels (dB)
  • P is the measured sound pressure, in Pa
  • The decibel is a dimensionless quantity based on
    the logarithm of a ratio and gives a more
    convenient range of values than would Pa

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Weighting Scales A, B, C
  • Each scale approximates the response of the human
    ear at different ranges of pressure
  • Because the human ear does not hear sound as if a
    machine. The human ear is more sensitive to
    higher frequencies
  • Derived from comparison experiments
  • Example a noise of 1000 Hz frequency and an SPL
    of 20 dB sounds as loud as a noise of 25 dB at
    500 Hz
  • A-Scale is most common and referenced by OSHA
  • B-Scale rarely used (medium sound pressure
  • C-Scale common for evaluating explosions and
    impact noise

Anatomy of the Ear
  • Outer ear and ear canal directs and amplifies the
    sound by 10-15 dB
  • Sound pressure waves impact on the ear drum and
    vibrate the three tiny bones in the middle ear
  • Malleus (hammer)
  • Incus (anvil)
  • Stapes (stirrup)
  • Which vibrates against the oval window leading to
    the inner ear

Inner Ear
  • Cochlea (inner ear)
  • Basilar membrane (lining of the cochlea)
  • Supports 25,000 specialized hair cells
  • Which send characterizing nerve impulses to the
  • Three semicircular canals (in orthogonal planes)
  • Filled with fluid
  • Provides sense of balance and relative body
  • Have you ever felt dizzy?
  • Eustachian tube
  • Connects middle ear to throat
  • Equalizes pressure
  • Have your ears ever popped?

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Hearing Loss
  • Conductive hearing loss
  • Interruptions along the pathway reducing hair
  • Excessive earwax, otitis media (fluid in middle
    ear), ruptured eardrum
  • Sensory hearing loss
  • Presbycusis (loss due to age)
  • Noise-induced hearing loss
  • Sociacusis (loss from everyday life)
  • Nosacusis (loss from disease, heredity, drugs,
    sudden and severe pressure changes, traumatic
    head injuries)
  • Tinnitus (follows traumatic exposure to loud
    noise perceived ringing, roaring, hissing may
    be permanent)

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Evaluating Hearing Ability and Hearing Loss
  • Audiograms
  • A hearing evaluation exam, called audiometry,
    produces a report called an audiogram
  • OSHA requires all workers exposed to an 8-hour
    TWA of at least 85 dBA (Action Level) receive a
    baseline audiogram and annual follow-up exam
  • Employee sits in soundproof booth with headphones
    and control button to produce HTL (Hearing
    Threshold Level)
  • Method of Limits at the following test
    frequencies 500, 1000, 2000, 3000, 4000, 6000
    Hz, the range most detectable by the human ear
  • Speech range 1000 4000 Hz

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Reasons for Variation in Audiometric Testing
  • Ear wax buildup
  • Head cold, congestion
  • Confusion about response procedure
  • Incorrect placement of headphones
  • Hair under headphones
  • Audiometer malfunction

OSHA Occupational Noise Exposure Standard
  • 29 CFR 1910.95
  • Requirements for maintaining and calibrating
    audiometric equipment and technician training
  • Table G-16A of Appendix A
  • Relates A-weighted sound level to allowed
  • Table A-1 of Appendix A
  • Converts Noise Exposure (Dose) to 8-hour TWA

Quantifying Hearing Loss
  • Watch for changes in the HTL (Hearing Threshold
  • STS (Standard Threshold Shift) decrease of 10
    db or more at 2000, 3000, or 4000 in either ear
  • Represents permanent hearing loss
  • Call for a re-test (after at least 14 hours of
    relative quiet)
  • TST (Temporary Threshold Shift) a shift in HTL
    that disappears after the person has been in a
    quiet environment for a few hours

Standard Threshold Shift (STS)
  • If an STS is identified
  • Notify the employee in writing
  • Provide additional training
  • Provide adequate hearing protection
  • Workers Compensation
  • Realize that WC laws for identifying and
    compensating STS will vary across the states

29 CFR 1910.95
  • Enacted in 1971
  • Hearing Conservation Program is required whenever
    employee exposures exceed 85 dBA 8-hr TWA
  • This is half the allowable noise exposure for an
    8 hour day or 50 Daily Noise Dose (DND)
  • Note 90 dBA for an 8-hr TWA is 100 DND

Hearing Conservation Program Elements
  • Exposure monitoring
  • Audiometric testing
  • Hearing protective devices
  • Training program
  • Access to the written standard
  • Recordkeeping

Measuring Occupational Noise
  • Sound Level Meters (SLM)
  • Used for area surveys
  • Settings for average, peak, impulse, ABC scales
  • Noise Dosimeters
  • Used for individual monitoring
  • Clip microphone near the ear
  • Wear all day
  • Calibrate before and after

Adding Decibels
  • Often there is a need to combine two or more
    noise sources
  • Because decibels are logarithms, they cannot be
    added directly
  • 80 dB 85 dB ? 165 dB
  • 80 dB 85 db 86 dB

  • Given three machines in a room measured at 80,
    85, and 87 dB, respectively
  • SPLtotal 10 log (1080/101085/101087/10)
  • SPLtotal 89.6 dB

Computing Daily Noise Doseand Calculating 8-hr
  • OSHA limits workers to 100 of the daily dose or
    90 dBA for 8-hr TWA
  • D 100 (C1/T1 C2/T2 Cn/Tn)
  • D daily nose dose, in percent
  • C total time of exposure at the measured noise
  • T reference allowed duration for that noise
    level from Table G-16a of Appendix A of 29 CFR

  • A workers exposure was monitored for 2 hrs at 80
    dBA, 2 hr at 85 dBA, and 4 hr at 87 dBA. What is
    the DND (Daily Noise Dose)?
  • D 100 (2/32 2/16 4/12.1) 51.8
  • The worker received 51.8 of their DND. (This is
  • Given a DND 51.8, find the 8-hr TWA.
  • Go to Table A-1. Round to 55 (conservative).
    Yields 85.7 dB TWA. The Hearing Conservation
    Program is required.

Controlling Noise
  • Engineering Controls
  • Administrative Controls
  • PPE

Engineering Controls
  • You can make a career out of engineering
    controls for controlling noise
  • Devices insulative curtains coverings for
    noise-reflective floors, ceilings, walls
    vibration isolation devices
  • Remember sound is a wave and cannot turn around
    corners this is the concept of directivity
  • Reflection sound waves can bounce back and
    add sound pressure at the source
  • Resonance a material vibrates at the same
    frequency as the emitted sound use an
    vibration isolator or rubber mounting

Engineering Controls
  • Some surfaces absorb the sound energy, or do
    not allow it to reflect effectively
  • Noise control curtains fiber-filled cloth office
  • Proper preventative maintenance (PM) on
    machines parts such as motors, bearings, drive
    belts, pumps, etc.
  • Adjustments, lubrication, replacement, vibration
  • Think outside the box for new designs and work
    with suppliers
  • One of the best engineering controls is
  • The relationship between noise and distance
    follows the inverse square law
  • Doubling the distance reduces the noise by ¼
  • Tripling the distance reduces the noise by 1/9

Administrative Controls
  • Used when engineering controls are exhausted or
  • Limiting time in exposed areas worker rotation
    limiting the number of workers in exposed areas
    (limited access)

Hearing Protective Devices (HPD)
  • After engineering and administrative controls are
    exhausted and infeasible
  • All workers exposed at 85 dBA for 8-hr TWA must
    be provided HPD at no cost
  • Employers must ensure workers actually wear the
  • Employers must provide a variety of HPD

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HPD Continued
  • Employers must train workers to use HPD and how
    to care for them
  • HPD attenuation must effectively reduce noise
    exposure to below the OSHA action level (85 dBA)
  • Noise Reduction Rating (NRR)
  • Typically 22 30 dB NRR
  • Numerical attenuation value determined in a
  • When using the A-Scale, you must deduct 7 dB from
    the NRR
  • When using the C-Scale, no deduction is necessary

  • Worker is exposed to 98 dBA for 8-hr TWA.
    Earplugs are available with a 29 NRR and earmuffs
    are available with a 25 NRR.
  • Since A-Scale, Earplugs (NRR 29-7 22) and
    Earmuffs (NRR 25-7 18)
  • Earplugs 98 22 76 dBA
  • Earmuffs 98 18 80 dBA
  • Both are below the 85 dBA 8-hr TWA Action Limit

Extreme Exposures
  • For extreme exposures with 8-hr TWA in excess of
    100 dBA, it may be necessary to use both earplugs
    and earmuffs
  • Their NRRs are not additive
  • Tests show an additional 3 10 dB NRR is
    achieved with the second device

  • Nims DK. Basics of Industrial Hygiene. John
    Wiley Sons, Inc., 1999. ISBN 0471-29983-9

  • Exercises Study Questions
  • P. 195, 1-39, divisible by 5
  • Research Exercises/Stds Questions
  • P. 199, 40-46, pick one
  • Exercises Study Questions
  • P. 224, 1-27, divisible by 5
  • Research Exercises/Stds Questions
  • P. 227, 28-33, pick one
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