Chapter 3_Industrial Hygiene for chemical industries.ppt

Industrial Hygiene

1. CHAPTER-3
Industrial Hygiene
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2. Typical projects involving industrial hygiene
•monitoring toxic airborne vapor concentrations,
•reducing toxic airborne vapors through the use of ventilation
• selecting proper personal protective equipment to prevent worker
exposure, developing procedures for the handling of hazardous materials,
and
• monitoring and reducing noise, heat, radiation, and other physical factors
to ensure that workers are not exposed to harmful levels.
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Industrial Hygiene Subject Matter
•What, How much, What is to be done???
•Identification of Hazards
–experience
–study
–defined by client
•Evaluation of Hazards
–Monitoring: sample collection & analysis
•Control of Hazards
–engineering, admin., work practices, PPE

4. Occupational Health Team
•Occupational Physicians
•Industrial or ”occupational” Hygienists
•Occupational Health Nurse
•Microbiologist
•Engineers
•Safety Personnel
•Ergonomists
•Chemists & Lab Personnel
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5. Identification
The sources of information include
•process design descriptions,
• operating instructions,
• safety reviews,
• equipment vendor descriptions,
• information from chemical suppliers, and
• information from operating personnel.
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The quality of this identification step is often a function of the number of
resources used and the quality of the questions asked.

6. Material Safety Data Sheets
MSDSs are available from
•the chemical manufacturer,
•a commercial source, or
•a private library developed by the chemical plant.
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•Manufacture's name
•Hazardous ingredients
•Physical/chemical characteristics
•Fire and explosion hazard data
•Precautions for safe handling
•Control measures
•Reactivity data
•Health hazard data

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9. Evaluation
The evaluation phase determines the extent and degree of employee
exposure to toxicants and physical hazards in the workplace environment.
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Evaluating Exposures to Volatile Toxicants by
Monitoring

10. for intermittent samples
Drawbacks
(1) the workers move in and out of the exposed workplace and
(2) the concentration of toxicants may vary at different locations in
the work area.
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11. If more than one chemical is present in the workplace
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exceeds 1, then the workers are
overexposed.

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mix
n
1i
i
TWA)(TLVC 


13. Estimating Worker Exposures to Toxic Vapors
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At steady state

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18. Estimating the Vaporization Rate of a Liquid
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21. Evaporation and displacement from a filling vessel
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Evaporation rate
the mass rate of volatile displaced
For splash filling
1
For subsurface filling 5.0

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25. Inherent Safety
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•An inherently safe plant relies on chemistry and physics to prevent
accidents rather than on control systems, interlocks, redundancy, and
special operating procedures to prevent accidents.
•The safety of a process relies on multiple layers of protection. The
first layer of protection is the process design features. Subsequent
layers include control systems, interlocks, safety shutdown systems,
protective systems, alarms, and emergency response plans. Inherent
safety is a part of all layers of protection.

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31. Respirators
•on a temporary basis, until regular control methods can be implemented;
•as emergency equipment, to ensure worker safety in the event of an
accident;
•as a last resort, in the event that environmental control techniques are
unable to provide satisfactory protection.
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33. Ventilation
•Ventilation can quickly remove dangerous concentrations of flammable
and toxic materials.
•Ventilation can be highly localized, reducing the quantity of air moved and
the equipment size.
•Ventilation equipment is readily available and can be easily installed.
•Ventilation equipment can be added to an existing facility.
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34. Ventilation is based on two principles
•dilute the contaminant below the target concentration, and
•remove the contaminant before workers are exposed.
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35. Local Ventilation
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36. advantages of enclosed hoods
•completely eliminate exposure to workers,
•require minimal airflow,
•provide a containment device in the event of fire or explosion, and
•provide a shield to the worker by means of a sliding door on the hood.
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disadvantages of hoods
•limit workspace and
•can be used only for small, bench-scale or pilot plant equipment.

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38. Dilution Ventilation
The following restrictions should be considered before implementing dilution
ventilation:
•The contaminant must not be highly toxic.
•The contaminant must be evolved at a uniform rate.
•Workers must remain a suitable distance from the source to ensure
proper dilution of the contaminant.
•Scrubbing systems must not be required to treat the air before exhaust
into the environment.
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39. PROBLEMS
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1 Air contains 4 ppm of carbon tetrachloride and 25 ppm of 1, l-dichloroethane.
Compute the mixture TLV, and determine whether this value has been exceeded.
2 Benzene and toluene form an ideal liquid mixture. A mixture composed of 50 mol %
benzene is used in a chemical plant. The temperature is 80°F, and the pressure is 1
atm. [P
sat
benzene= 104 mm Hg, P
sat
Toluene=30.9 mm Hg]
a. Determine the mixture TLV
b. Determine the evaporation rate per unit area for this mixture.
c. A drum with a 2-in-diameter bung is used to contain the mixture. Determine the
ventilation rate required to maintain the vapor concentration below the TLV. The
ventilation quality within the vicinity of this operation is average.
3 A drum contains 42 gal of toluene. If the lid of the drum is left open (lid diameter = 3
ft), determine the time required to evaporate all the toluene in the drum. The
temperature is 85°F. Estimate the concentration of toluene (in ppm) near the drum if
the local ventilation rate is 1000 ft
3
/min. The pressure is 1 atm.
4 A certain plant operation evaporates 2 pint/hr of toluene and 1 pint18-hr shift of
benzene. Determine the ventilation rate required to maintain the vapor concentration
below the TLV. The temperature is 80°F, and the pressure is 1 atm.
5 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 cm
2
. Estimate the ambient vapor
concentration if the ventilation rate is 3000 ft
3
/min. The vapor pressure of 2-
butoxyethanol is 0.6 mm Hg under these conditions.

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