Industrial Hygiene - PowerPoint PPT Presentation

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Industrial Hygiene

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Title: Industrial Hygiene


1
Industrial Hygiene
  • Exposure Evaluation and Control

2
Industrial Hygiene -Exposure Evaluation and
Control
  • Industrial hygiene is defined as the
    anticipation, identification, evaluation and
    control of occupational conditions which cause
    sickness and/or injury

3
Industrial Hygiene -Exposure Evaluation and
Control
  • Exposure Evaluation
  • Measurement techniques
  • Estimating exposure
  • Open tanks
  • Filling tanks
  • Control Techniques
  • Personal Protection

4
Evaluation of Chemical Hazards
  • Detector tubes - color change for specific
    species
  • Adsorption tubes sample air drawn through
    adsorbent then released into GC
  • Filters collects particulate dust and fibers
  • Portable monitors hand held monitors to look
    for leaks or hot spots
  • Real time monitors used to determine average,
    maximum and minimum concentrations.
  • Personal monitors used to determine exposure of
    worker

5
Air Monitoring Strategies
  • Determine worker exposure
  • Variable concentration
  • Contamination level
  • Control measures
  • Batch operations
  • Air circulations patterns
  • Seasonal variations

6
Exposure Evaluation
  • Threshold Limit Value - Time Weighted Average,
    TLVTWA
  • tw is the length of shift
  • tn is 8 hours

7
Exposure Evaluation
  • Intermittent monitoring
  • I number of measurements during shift
  • is the time period over which measurement
    i is taken
  • Assume concentration is constant during the
    time period

8
Exposure Evaluation
  • Multiple Toxicants
  • N is total number of toxicant
  • Cn is the concentration relative to other
    toxicants
  • Here we assume the effects are additive

9
Estimating Exposure from Open Tanks
  • Author derives relationships assuming no
    toxicants in ventilation air. I will present of
    more complete analysis.

10
Mass Balance on Room for Toxic Vapor
11
Estimating Exposure from Open Tanks (cont.)
  • Assume Steady State
  • Assume Nonideal mixing
  • Cout kCmax
  • k1 for perfect mixing
  • Table 3-11 gives values of k, worst case
    scenario is k?1/10

12
Estimating Exposure from Open Tanks (cont)
  • Substituting

13
Estimating Exposure from Open Tanks (cont)
  • Air mass balance
  • Assume steady state

14
Estimating Exposure from Open Tanks (cont)
  • Assume ideal gas and that toxic vapor has
    negligible mass compared to mass of air
  • Set equal, so

15
Estimating Exposure from Open Tanks (cont)
  • Substituting
  • Qv,out ? 3000 ft3/min for out doors

16
Estimating Exposure from Open Tanks (cont)
  • Now estimate evaporation rate diffusion away
    from the liquid surface
  • M is molecular weight
  • K is mass transfer coefficient (length/time)
  • A is surface area over which driving force exists
  • TL is absolute temperature of volatile liquid
  • is partial pressure above surface
  • Worst case Psatgtgtgt

17
Estimating Exposure from Open Tanks (cont)
  • Substituting
  • With simplifying assumptions you get
  • Eq 3-14

18
Estimating Exposure from Open Tanks (cont)
  • Correlation for mass transfer coefficients
  • For water M018 and K00.83cm/sec

19
Estimating Exposure from Filling Tank
20
Estimating Exposure from Filling Tank (cont)
  • Assume vapor space above liquid is partially
    saturated
  • With a heal left in vessel ? 1

21
Estimating Exposure from Filling Tank (cont)
  • displacement diffusion out of tank
  • Assume worst case ltlt Psat

22
Estimating Exposure from Filling Tank (cont)
  • Similar to, but better, than Eq. 3-24

23
Textbook Error
  • Note that Example 3-9 on page 68 has error
  • 7.481gal/ft3 is correct not 7.481 ft3/gal

24
Control of Chemical Hazards
  • Engineering Control
  • Administrative Control
  • Protective Equipment

25
Engineering Controls
  • Inherent Safety
  • Containment
  • Ventilation

26
Inherent Safety Aspects
  • Substitution
  • Use chemicals and equipment which are less
    hazardous
  • Attenuation
  • Use chemicals under conditions which make them
    less hazardous
  • Isolation
  • Isolate equipment and/or sources of hazard
  • Intensification
  • Reduce quantity of chemical

27
Containment Principles
  • Containment refers to keeping the process
    materials contained within the processing
    equipment
  • Design for internal deflagration
  • Vent to containment or control equipment
  • Use rupture disks or safety valves to vent
    excessive pressure spikes
  • Venting to containment vessel or flare, etc.

28
Containment PrinciplesSealing Points and Leak
Protection
  • Static Seals
  • Welds
  • Flanges
  • Covers/Heads
  • Welds are better than flanges
  • Dynamic Seals
  • Relative motion between seal parts
  • Rotating Shafts
  • Valve stems

29
Containment PrinciplesRotating Shaft Sealing
Methods
  • Stuffing Box and Packing
  • Mechanical Seal
  • Double Mechanical Seal
  • Allows evacuation between seals
  • Seal Maintenance procedure required

30
Avoiding Dynamic Seals
  • Seal-less pump
  • Magnetic coupling
  • Canned rotor
  • Diaphragm
  • Bellows-Seal Valve

31
Potential Leakage Locations/Occasions
  • Sight glasses
  • Gage glasses
  • Sampling points
  • Addition points
  • Batch processing vessels
  • Loading/Unloading
  • Packaging
  • Maintenance

32
Ventilation for Control
  • Outdoor construction
  • Local Ventilation
  • Dilution Ventilation

33
Local Exhaust Ventilation
  • Removes contaminants at source
  • Prevents toxic material from entering the
    workplace air
  • Requires less airflow than dilution ventilation

34
Components of a Local Exhaust Ventilation System
  • Hood or Elephant Trunk
  • Duct system
  • Air cleaning system
  • Air mover
  • Outlet

35
Hood Ventilation
  • Totally Enclosed
  • Enclosed structure around processing equipment
    with limited (No) access. Emissions taken to be
    treated
  • Exterior Hood
  • Also called Elephant Trunk. Duct inlets
    located close to source. Often flexible duct
    that can be moved some, i.e. elephant trunk.

36
Hood Ventilation - Booth
  • Booth Hood
  • Standard fume hood seen in laboratories
  • Need to keep the window always slightly opened to
    ensure there is some are flow

37
Hood Ventilation - Booth
  • Booth Hood
  • Bypass laboratory hood ensures that there is
    always a positive flow through the hood and
    minimizes the circulation patterns that might
    allow fumes to be released

38
Negative Ventilation Systems
  • Need to keep exhaust system under negative
    pressure so that any leakage will be from the
    rooms into the exhaust system and not vice versa.

39
Duct System Design
  • Basic fluid mechanics
  • Publications/Recommendations
  • Capture velocity
  • Entrainment velocity
  • Pressure losses

40
Dilution Ventilation
  • Air flow throughout building
  • High air flow required
  • Best used in conjunction with localized hooding
  • Integrated with local HVAC system

41
Ventilation Exhaust May Require Cleaning
  • Absorption
  • Adsorption
  • Flare or Incineration
  • Stack to prevent re-entry
  • Best to treat localized exhaust system,
    prohibitive to treat a dilution ventilation
    system.

42
Administrative Control Techniques
  • Work Rules to Limit Exposure Time and/or limit
    accessibility to areas with high concentrations.
  • Good Housekeeping
  • Functional Operating and Maintenance Procedures
  • Education and Training of all personnel

43
Good Housekeeping
  • Keeps toxics and dusts contained
  • Use dikes around tanks and pumps
  • Provide water and steam connections for area
    washing
  • Provide lines for flushing and cleaning
  • Provide well-designed sewer system with emergency
    containment

44
Elements of PPE Training Program
  • Standard and regulatory requirements
  • Hazard characterization in the workplace
  • Implementation of engineering and management
    controls
  • Description of need, capabilities and limitations
    of PPE
  • Demonstration of proper use, fit, care,
    maintenance and repair of PPE
  • Explanation of PPE written policy, regulations
    and enforcement
  • Discussion of record-keeping requirements

45
Personal Protective Equipment
  • Engineering and Management controls can reduce or
    even eliminate many occupational safety hazards.
    However, it may be impractical or impossible to
    keep the work area completely free of
    contaminants or to keep all workers away from
    dangerous locations.
  • PPE is the last line of defense

46
Personal Protective Equipment
  • Routine Equipment
  • Emergency

47
Protection of the Head
  • Hard hats should be able to withstand the impact
    of a 8 lb iron ball dropped from 5 feet
  • Should be non conducting

48
Eye Protection
  • Unvented goggles
  • Impact resistant lenses
  • and side shields
  • Chemical splash
  • goggles

49
Hearing Protection
  • Ear plugs
  • Range from 17 - 25 dB
  • Hearing bands allow on-off use
  • Earmuffs
  • Provide wide range of protection from 19 to 30 dB

50
Respirators
  • Dust and mist respirators
  • Filter out particulate
  • Need to have ambient oxygen
  • Does not stop vapors or gases

51
Respirators
  • Air-Purifying Respirators
  • Adsorbent removes gas, vapor, or particulate
  • Different cartridges for different types of vapor
  • Needs to
  • have ambient
  • oxygen

52
Respirators
  • Supplied Air
  • Unlimited air supply from remote site
  • Requires compressor
  • Disadvantage of possible damage to hose, limited
    mobility and contamination from compressor

53
Respirators
  • Self Contained (SCBA)
  • Avoids problems of supplied air
  • Limited supply
  • Typically used for emergency operation

54
Respirators
  • All respirators need to be fit properly and
    tested routinely to ensure that they function.
  • Emergency respirators need to be serviced
    routinely to ensure that they function when
    needed.

55
Protective Clothing
  • Gloves
  • Boots
  • Trousers
  • Slickers
  • Full body protection

56
Chemical Engineers Responsibilities
  • Engineer leadership
  • Legal responsibility
  • Ethical responsibility

57
Safety
  • Safety needs to become a mindset and a way of
    life for a practicing engineer.

58
In Class Problem
  • As a homework team solve the following problem
  • Fifty-five gallon drums are being filled with
    2-butoxyethanol. The drums are being splash
    filled at the rate of 30 drums per hour. The
    bung opening through which the drums are being
    filled has an area of 8 cm2. Estimate the vapor
    concentration (in ppm) if the ventilation rate is
    3000 ft3/min. The molecular weight of
    2-butoxyethanol is 118 and the vapor pressure is
    0.6 mm Hg at these conditions.

59
Solution
  • M118 lbm/lbmol
  • Po0.6 mmHg
  • Qv3000 ft3/min
  • TLTa
  • Area8 cm2
  • Filling rate 30drum/hr
  • F1.0 (splash filling)
  • V55gal

Design Equation
Similar to Eq 3-24
60
Solution continued
Find mass transfer
Filling rate
61
Solution continued
However,
So
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