Industrial Hygiene ERT 312 Lecture 7 – Identification, Evaluation and Control

Identification  Able to identify the hazard from single exposure or potential combined effects from multiple exposures  Require deep study on the chemical process, operating conditions and operating procedures  Source of information;  Process design descriptions  Operating instructions  Safety reviews  Equipment specs  Etc. 2

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Material Safety Data Sheets (MSDS)  Chemical Safety Data Sheets (CSDS)  MSDS lists the physical properties of a substance that may be required to determine the potential hazards of the substance  Manufacturer/supplier is responsible to provide the MSDS to their customers * Example of MSDS 5

Evaluation  To determine the extent and degree of employee exposure to toxicants and physical hazards in the workplace  Once exposure data obtained, comparison is being made to acceptable occupational health standards eg: TLVs, PELs and IDLH concentrations (page 56)  Then, the decision on proper control measure can be made accordingly in order to reduce the risk 6

 Threshold Limit Value (TLV) of a chemical substance is a level to which it is believed a worker can be exposed day after day for a working lifetime without adverse health effects  The Permissible Exposure Limit (PEL or OSHA PEL) is a legal limit for exposure of an employee to a substance or physical agent. For substances it is usually expressed in parts per million (ppm), or sometimes in milligrams per cubic metre (mg/m 3 )legal substanceparts per million milligramscubic metre  IDLH is an initials for Immediately Dangerous to Life and Health, and is defined by the NIOSH as exposure to airborne contaminants that is "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment”NIOSH 7

Table 2.7 – established by ACGIH 8

 TLVs units – ppm, mg/m 3,  For dust – mg/m 3 or mppcf  For vapors, concentration in ppm;  Cppm = =  T (temperature, Kelvin), P (absolute pressure, atm) M (molecular weight, g/g-mol) Equation 1 Equation 2 9

Problem 2.7 (Crowl & Louvar, 2002)  How much acetone liquid (ml) required to produce a vapor concentration of 200 ppm in a room of dimension 3 x 4 x 10 m? Given T is 25°C, P is 1 atm, molecular weight is 58.1 and specific gravity is

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Evaluation Exposure of Organic Toxicants  The simplest way to determine worker exposures is through continuous monitoring of the air concentrations.  For computation of continuous concentration data C(t) the TWA concentration,  C(t)the concentration of the toxicant in the air, mg/m 3  twthe worker shift time in hours Equation 3 12

 Sometimes, continuous monitoring is not feasible. Therefore, intermittent samples representing worker exposure at fixed points of time are obtained. Single Component Exposure, workers are overexposed if the sum of conc. > permitted TWA Equation 4 13

Example 3.3 (Crowl & Louvar, 2002)  Determine the 8-hr TWA worker exposure if the worker is exposed to toluene vapors as follows; Solution: Answer: 155 ppm Duration (h)Concentration (ppm) Equation 5 14

 For a case of more than 1 toxicant is present in the workplace; the combined exposures from multiple toxicants with different TLV-TWAs is determined by;  nthe total number of toxicants  C i the conc. of toxicant i with respect to the other toxicants  (TLV-TWA) i the TLV-TWA for toxicant sp. i If the sum of the equation > 1, workers are overexposed Equation 6 15

 The mixture also TLV-TWA can be computed using equation below; If the total mixture conc. > (TLV- TWA) mix, workers are overexposed Equation 7 16

Example 3.2 (Crowl & Louvar, 2002) Air contains 5 ppm of diethylamine (TLV-TWA = 10 ppm), 20 ppm cyclohexanol (TLV-TWA = 50 ppm) and 10 ppm of propylene oxide (TLV-TWA = 20 ppm). What is the mixture TLV-TWA and has this level been exceeded? 17

Evaluation of exposure to dusts  Dusts particle size range of µm  Particles > 0.5 µm unable to penetrate the lungs  Particle < 0.2 µm settle out too slowly, most exhaled with the air  Units: mg/m mg/mppcf Equation 8 18

Example 3-5 (Crowl & Louvar, 2002)  Determine the TLV for a uniform mixture of dusts containing the following particles;  Solution:  Answer: 6.8 mppcf Type of dustConcentration (wt.%) TLV (mppcf) Nonasbestiform7020 Quartz

Evaluation of exposure to Noise  Noise levels are measured in decibels (dB)  A dB is a relative logarithmic scale used to compare the intensities of two sounds. If one sound is at intensity I and another sound is at intensity I o, then the difference in intensity levels in dB is given; Noise intensity (dB) = - 10 log 10 (I/I o ) 20

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Example 3.6 (Crowl & Louvar, 2002) Determine whether the following noise level is permissible with no additional control features: Noise Level (dBa)Duration (hr)Max. allowed (hr) 853.6No limit

Solution: (TLV – TWA) mix, noise = The sum > 1.0, workers are immediately required to wear ear protection. For long term plan, noise reduction control should be applied. 23

Evaluation of exposure to Toxic Vapors Ventilation rate, Q v (volume/time) Volatile rate out, kQ v C (mass/time) Evolution rate of volatile, Q m (mass/time) Enclosure volume, VVolatile concentration, C (mass/volume) Equation 9 24

Assumptions  The calculated concentration is an average concentration in the enclosure. Localized conditions could result in significantly higher concentrations; workers directly above an open container might be exposed to higher concentrations  A steady-state condition is assumed; that is, the accumulation term in the mass balance is 0  The non-ideal mixing factor, k varies from 0.1 – 0.5 for most practical situations. For perfect mixing, k = 1 25

Example 3.7 (Crowl & Louvar, 2002) An open toluene container in an enclosure is weighed as a function of time, and it is determined that the average evaporation rate is 0.1 g/min. the ventilation rate is 100 ft 3 /min. the temperature is 80 o F and the pressure is 1 atm. Estimate the concentration of toluene vapor in the enclosure, and compare your answer to the TLV for toluene of 50 ppm. 26

Solution  Use equation 9 to solve the problem From data given; Qm0.1 g/min Rg ft 3.atm/lb-mol. o R T80 o F = 540 o R Qv100 ft 3 /min M92 lb m /lb-mol P1 atm k? Answer:kC ppm = 9.43 ppm K varies from 0.1 – 0.5, therefore Cppm may vary from 18.9 – 94.3 ppm. Actual vapor sampling is recommended to ensure that TLV is not exceeded 27

Estimating the vaporization rate of a liquid QmQm QmQm Volatile Substances Open Vessel Chemical Spill 28

 General expression for vaporization rate, Q m (mass/time):  MMolecular weight of volatile substance  Kmass transfer coefficient (length/time) for an area A  R g ideal gas constant  T L absolute temperature of the liquid Equation 10 29

 For most cases, P sat >> p;  The equation is used to estimate the evaporation rate of volatile from an open vessel or a spill of liquid Equation 11 30

 To estimate the concentration of volatile in enclosure resulting from evaporation of a liquid;  Kgas mass transfer coefficient Most events, T = T L Equation 12 Equation 13 Equa. 11 used in Equa.9 31

 Estimation of K, gas mass transfer coefficient;  aconstant  Dgas-phase diffusion coeeficient Equation 14 32

 To determine the ratio of the mass transfer coefficient between species K and a reference species K o ;  The gas-phase diffusion coefficients are estimated from the molecular weight, M of the species; Equation 15 Equation 16 33

 Combined equation 15 & 16, simplified;  K water 0.83 cm/s Equation 17 34

Example 3.8 (Crowl & Louvar, 2002)  A large open tank with a 5-ft diameter contains toluene. Estimate the evaporation rate from this tank assuming a temperature of 77 o F and a pressure of 1 atm. If the ventilation rate is 3000 ft 3 /min, estimate the concentration of toluene in this workplace enclosure. 35

Evaluation of exposure during vessel filling operations  For this case, volatile emissions are generated from 2 sources:  Evaporation of a liquid, (Q m ) 1  Displacement of the vapor in the vapor space by the liquid filling the vessel, (Q m ) 2  Therefore, the net generation of volatile; (Q m ) = (Q m ) 1 + (Q m ) 2 Equation 18 36

37 Vapor Liquid Volatile in Vessel Total Source = Evaporation + Displaced Air Evaporation

r f constant filling rate of the vessel (time -1 )  v density of the volatile vapor Equation 19 Equation 20 38

 Hence, the net source term; Equation 20 Equation 21 39

Problem 3.24 (Crowl & Louvar, 2002) 55-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 for 2-butoxyethanol is 0.6 mm Hg under these conditions. 2-butoxyethanol chemical formula: HOCH 2 C 2 HOC 4 H 9 40

Solution: 41

Appendix A 42

Appendix B  Conversion of Fahrenheit (°F) to Rankine (°R) 1 st step Convert Fahrenheit to Celcius 2 nd step Convert Celcius to Kelvin 3 rd step Convert Kelvin to Rankine 43