Introduction to Industrial Hygiene

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Introduction to Industrial Hygiene

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

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Introduction to Industrial Hygiene

• Read Asfahl
• Chapter 9, Health and Toxic Substances
• Chapter 10, Environmental Control and Noise

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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

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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

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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
  potential
• In the far past, causes were not always recognized

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Earliest Recordings

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

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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

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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

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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)

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Paracelsus

• 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.

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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

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Bernardino Ramazzini (1633-1714)

• Wrote a book, De Morbis Artificum (Diseases of
  Workers), starting the field of occupational
  medicine
• 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
  laundresses.

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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

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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
  hats
• Bars were installed on windows at hat factories
  presumably to prevent afflicted workers from
  leaping during bouts of depression

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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.

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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

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Industrial Hygiene

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

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Professional Organizations

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

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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

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Control of Agents

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

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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

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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

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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.

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4. Recordkeeping

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

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5. Employee training

• Effective component if total program is
  implemented and engineering controls are first
  established
• 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,
  effectiveness

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6. Program review

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

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Toxicology

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Definitions

• 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

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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

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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
  response

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Definitions

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

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Dose Response Curve
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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

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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
  organism
• 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

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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

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LD50 Relative Toxicity
Agent LD50 (mg/kg)
Ethyl Alcohol 10,000
Sodium chloride 4,000
Morphine sulfate 900
Strychnine sulfate 2
Nicotine 1
Hemicholinium-3 0.2
Dioxin (TCDD) 0.001
Botulinum toxin 0.00001
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Effect of route of administration
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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

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Epidemiological Studies

• Prospective epidemiological study
• Take a cohort (or group of individuals) with a
  common exposure
• Follow through time to see if they develop
  disease
• 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

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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
  valuable

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Routes of Exposure

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

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Inhalation

• 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
  bloodstream

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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
  exist
• Lighting cigarettes with dirty hands
• Application of cosmetics
• Use of chewing tobacco or gum in contaminated
  areas

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Ingestion

• 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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Injection

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

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Absorption into eyes and ears

• Much less common but possible
• Moist surfaces

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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

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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
  concentration
• Active transport
• Movement across a membrane otherwise impermeable
  by a transport mechanism
• Chemical reaction or carrier molecule, requires
  energy
• Phagocytosis
• Toxins eat or engulf other cells or by use of
  white blood cells

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Liver

• Important in metabolism, energy storage, protein
  synthesis
• 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

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Kidneys

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

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Classes of Toxins and Toxic Responses

• Irritants and Sensitizers
• Systemic Toxins
• Neurotoxins
• Reproductive Toxins
• Carcinogens

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Occupational Health Standards

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Exposure Limits

• Mainly concerned with air quality values in the
  workplace
• 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.

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Sources of Exposure Limits

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

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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
  Tx
• 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

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

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Example PELs (Table Z-1)
Substance PPM Mg/m3
Ammonia 50 35
Carbon Dioxide 5000 9000
Carbon Monoxide 50 55
Chlorine (C) 1 (C) 3
Notes PELs are 8-hr TWA unless otherwise noted.
C refers to ceiling limit
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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
  min
• See 29CFR1910.1028 for more specific standards on
  benzene

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Carcinogens

• 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

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Respiratory Protection Standard

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

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Respiratory Std Cont.

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

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HAZWOPER

• Hazardous Waste Operations and Emergency Response
  Standard
• 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.

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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

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Occupational Noise Exposure Standard

• 29 CFR 1910.95

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Airborne Hazards

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Introduction

• 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

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Anatomy Function of the Lungs

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

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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

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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
  upward
• Cigarette smoking can paralyze the cilia
• Particle-laden mucus is removed by coughing,
  expectorating, or swallowing

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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
  particles
• Visible to human eye
• gt 100 mm 0.1 mm 0.01 cm
• Human hair diameter
• 5 500 mm 0.005 0.5 mm

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Protective Mechanisms of the Respiratory Tract

• Larger particles (gt10 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

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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
  them
• The smallest of particles may pass through cell
  membranes and lodge between cells (interstitial
  space)

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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,
  fumes
• Gases / vapors
• Gaseous contaminants, vapors
• Oxygen-deficient atmospheres
• lt 19.5 oxygen
• Combination
• Any combination of particulates and/or gases,
  including oxygen-deficient atmospheres

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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

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Occupational Diseases Associated with Airborne
Particulates

• Pneumoconiosis
• Physiological Responses
• Mineral Fibers and Other Fibers
• Metals
• Organic Particles

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Indoor Air Quality

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IAQ Outline

1. Introduction
2. Indoor air quality as a public health concern
3. Heating, ventilating, and air conditioning
   systems (HVAC)
4. Basic instruments for use in IAQ studies
5. Microorganism contamination and IAQ
6. Radon and asbestos

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Introduction

• 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

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Indoor Air Quality as a Public Health Concern

• The energy crisis in the 1970s spawned
  construction of thousands of energy efficient
  buildings
• Sealed windows
• Thermostats not accessible or adjustable by
  occupants
• Self-contained environments with controls for
  temperature, humidity, airflow
• Complaints odors, too hot, too cold
• Physical symptoms headaches, respiratory
  irritation

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Temperature

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

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Humidity

• 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

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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
  air
• Some areas benefit, other areas suffer
• Dead zones may allow odors and CO2 to accumulate
  to unacceptable levels

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Odors

• 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

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Physical Symptoms

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

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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
  microbes
• In 10 of the cases, no cause could be found

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Psychosocial Factors

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

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OSHA Standards for IAQ

• On December 17, 2001, OSHA withdrew its IAQ
  proposal and terminated rulemaking proceedings
• Proposed
• CO2 lt 800 ppm
• RH lt 60
• 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

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ASHRAE

• American Society of Heating, Refrigerating, and
  Air-Conditioning Engineers
• www.ashrae.org
• 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

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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

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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

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Occupational Noise Exposure

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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

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Introduction

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

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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
  steel
• Some materials will amplify or reflect sound
• Frequency (f) is related to pitch
• Healthy, young person can detect 20 to 20,000 Hz
  (cycles/sec)
• 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
  regs
• B-Scale rarely used (medium sound pressure
  levels)
• C-Scale common for evaluating explosions and
  impact noise

122
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

123
Inner Ear

• Cochlea (inner ear)
• Basilar membrane (lining of the cochlea)
• Supports 25,000 specialized hair cells
• Which send characterizing nerve impulses to the
  brain
• Three semicircular canals (in orthogonal planes)
• Filled with fluid
• Provides sense of balance and relative body
  position
• 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
  stimulation
• 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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128
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

131
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
  duration
• Table A-1 of Appendix A
• Converts Noise Exposure (Dose) to 8-hour TWA

132
Quantifying Hearing Loss

• Watch for changes in the HTL (Hearing Threshold
  Level)
• 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

133
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

134
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

135
Hearing Conservation Program Elements

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

136
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

137
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

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Example

• 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

139
Computing Daily Noise Doseand Calculating 8-hr
TWAs

• 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
  level
• T reference allowed duration for that noise
  level from Table G-16a of Appendix A of 29 CFR
  1910.95

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Example

• 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
  OK.)
• 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.

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Controlling Noise

1. Engineering Controls
2. Administrative Controls
3. PPE

142
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

143
Engineering Controls

• Some surfaces absorb the sound energy, or do
  not allow it to reflect effectively
• Noise control curtains fiber-filled cloth office
  partitions
• Proper preventative maintenance (PM) on
  machines parts such as motors, bearings, drive
  belts, pumps, etc.
• Adjustments, lubrication, replacement, vibration
  isolators
• Think outside the box for new designs and work
  with suppliers
• One of the best engineering controls is
  distance
• 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

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Administrative Controls

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

145
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
  HPD
• 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
  laboratory
• When using the A-Scale, you must deduct 7 dB from
  the NRR
• When using the C-Scale, no deduction is necessary

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Example

• 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

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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

150
References

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

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HW14

• 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