Title: Industrial Hygiene
1Industrial Hygiene
- Exposure Evaluation and Control
2Industrial 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
3Industrial Hygiene -Exposure Evaluation and
Control
- Exposure Evaluation
- Measurement techniques
- Estimating exposure
- Open tanks
- Filling tanks
- Control Techniques
- Personal Protection
4Evaluation 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
5Air Monitoring Strategies
- Determine worker exposure
- Variable concentration
- Contamination level
- Control measures
- Batch operations
- Air circulations patterns
- Seasonal variations
6Exposure Evaluation
- Threshold Limit Value - Time Weighted Average,
TLVTWA - tw is the length of shift
- tn is 8 hours
7Exposure 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
8Exposure Evaluation
- Multiple Toxicants
- N is total number of toxicant
- Cn is the concentration relative to other
toxicants - Here we assume the effects are additive
9Estimating Exposure from Open Tanks
- Author derives relationships assuming no
toxicants in ventilation air. I will present of
more complete analysis.
10Mass Balance on Room for Toxic Vapor
11Estimating 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
12Estimating Exposure from Open Tanks (cont)
13Estimating Exposure from Open Tanks (cont)
- Air mass balance
- Assume steady state
14Estimating Exposure from Open Tanks (cont)
- Assume ideal gas and that toxic vapor has
negligible mass compared to mass of air - Set equal, so
15Estimating Exposure from Open Tanks (cont)
- Substituting
- Qv,out ? 3000 ft3/min for out doors
16Estimating 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
17Estimating Exposure from Open Tanks (cont)
- Substituting
- With simplifying assumptions you get
- Eq 3-14
18Estimating Exposure from Open Tanks (cont)
- Correlation for mass transfer coefficients
- For water M018 and K00.83cm/sec
19Estimating Exposure from Filling Tank
20Estimating Exposure from Filling Tank (cont)
- Assume vapor space above liquid is partially
saturated - With a heal left in vessel ? 1
21Estimating Exposure from Filling Tank (cont)
- displacement diffusion out of tank
- Assume worst case ltlt Psat
22Estimating Exposure from Filling Tank (cont)
- Similar to, but better, than Eq. 3-24
23Textbook Error
- Note that Example 3-9 on page 68 has error
- 7.481gal/ft3 is correct not 7.481 ft3/gal
24Control of Chemical Hazards
- Engineering Control
- Administrative Control
- Protective Equipment
25Engineering Controls
- Inherent Safety
- Containment
- Ventilation
26Inherent 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
27Containment 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.
28Containment 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
29Containment PrinciplesRotating Shaft Sealing
Methods
- Stuffing Box and Packing
- Mechanical Seal
- Double Mechanical Seal
- Allows evacuation between seals
- Seal Maintenance procedure required
30Avoiding Dynamic Seals
- Seal-less pump
- Magnetic coupling
- Canned rotor
- Diaphragm
- Bellows-Seal Valve
31Potential Leakage Locations/Occasions
- Sight glasses
- Gage glasses
- Sampling points
- Addition points
- Batch processing vessels
- Loading/Unloading
- Packaging
- Maintenance
32Ventilation for Control
- Outdoor construction
- Local Ventilation
- Dilution Ventilation
33Local Exhaust Ventilation
- Removes contaminants at source
- Prevents toxic material from entering the
workplace air - Requires less airflow than dilution ventilation
34Components of a Local Exhaust Ventilation System
- Hood or Elephant Trunk
- Duct system
- Air cleaning system
- Air mover
- Outlet
35Hood 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.
36Hood 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
37Hood 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
38Negative 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.
39Duct System Design
- Basic fluid mechanics
- Publications/Recommendations
- Capture velocity
- Entrainment velocity
- Pressure losses
40Dilution Ventilation
- Air flow throughout building
- High air flow required
- Best used in conjunction with localized hooding
- Integrated with local HVAC system
41Ventilation 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.
42Administrative 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
43Good 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
44Elements 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
45Personal 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
46Personal Protective Equipment
- Routine Equipment
- Emergency
47Protection 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
48Eye Protection
- Unvented goggles
- Impact resistant lenses
- and side shields
- Chemical splash
- goggles
49Hearing 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
50Respirators
- Dust and mist respirators
- Filter out particulate
- Need to have ambient oxygen
- Does not stop vapors or gases
51Respirators
- Air-Purifying Respirators
- Adsorbent removes gas, vapor, or particulate
- Different cartridges for different types of vapor
- Needs to
- have ambient
- oxygen
52Respirators
- Supplied Air
- Unlimited air supply from remote site
- Requires compressor
- Disadvantage of possible damage to hose, limited
mobility and contamination from compressor
53Respirators
- Self Contained (SCBA)
- Avoids problems of supplied air
- Limited supply
- Typically used for emergency operation
54Respirators
- 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.
55Protective Clothing
- Gloves
- Boots
- Trousers
- Slickers
- Full body protection
56Chemical Engineers Responsibilities
- Engineer leadership
- Legal responsibility
- Ethical responsibility
57Safety
- Safety needs to become a mindset and a way of
life for a practicing engineer.
58In 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.
59Solution
- 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
60Solution continued
Find mass transfer
Filling rate
61Solution continued
However,
So