CHAPTER 9     SOLUTIONS TO END-OF-CHAPTER EXERCISES

 

 

 9.1.         To protect the firm from liability for pre-employment health conditions or pre-existing injuries or damage to tissues, such as lungs.

 

 9.2.         The term "toxic substances" generally refers to agents that cause harm to the body. Examples would be irritants, systemic poisons, depressants, asphyxiants, carcinogens, teratogens, and mutagens. "Hazardous materials" are more likely to be associated with safety hazards, such as fire and explosion hazards. Admittedly, toxic substances are also hazardous, but the terminology used by OSHA and practicing professionals is to make the above-described distinction between the two terms.

 

 9.3.         Irritants, systemic poisons, depressants, asphyxiants, carcinogens, teratogens, and mutagens.

 

 9.4.         Ethyl alcohol or "ethanol." Its principal hazard is as a depressant.

 

 9.5.         Inhalation, (skin) absorption, and ingestion.

 

 9.6.         Dentistry

 

 9.7.         For most toxic substances, OSHA has taken a general approach and has published "national consensus" PELs, based upon existing TLVs published by the American Conference of Governmental Industrial Hygienists (ACGIH). However, for some substances OSHA has gone much further and written "completed" standards, each addressing a particular substance. Prominent examples of such substances are asbestos and lead. Other prominent examples include benzene, vinyl chloride, cadmium, and arsenic. (See Table 9.1 of the text).

 

 9.8.         Odorless gases include carbon monoxide, carbon dioxide, methane, and nitrogen. Carbon monoxide is more dangerous than the others, but the others can be dangers as simple asphyxiants, crowding out life-giving oxygen. Methane is listed here as odorless, but usually, for safety reasons, the gas utility company adds a stanching agent, such as ethyl mercaptan, to make the methane have the characteristic "natural gas" odor.

 

 9.9.         Hydrogen sulfide, commonly known as "rotten-egg gas." The term "olfactory" refers to the sense of smell.

 

9.10.         AL represents the "Action Level," and PEL represents the "Permissible Exposure Level." The AL is usually 1/2 of the level of the PEL and is intended to be a warning level so that controls can be instigated before employee exposures exceed the legal limit prescribed by the PEL.

 

9.11.         "Solid" particles that are generally too fine to be called dusts.  Fumes are typically formed by the resolidification of vapors from very hot processes such as welding.

 

9.12.         0.033% is equivalent to 0.00033 x 106 = 330

 

              The PELs (TWAs) are found in Appendix A.1:

 

              PELs (ppm)

                           Carbon               Carbon

                           Monoxide             Dioxide

                             50                 5,000

 

                              Ci      330     x  

                     Em = S  -- = ------- + ---- < 1

                             Li     5000    50

                            

 

                            x < 1 - 330 

                           50         5000

 

                             x < 9670

                           50     5000

 

                           x < 9670(50)

                                  5000

 

                           x < 96.7 ppm carbon monoxide

 

 

9.13.         Concentration Length of Time       C x Ti

                     .00001        4 hr                 .00004

                     .00015        4 hr                 .00060

 

                     Total         8 hr                 .00064

 

                     S CiTi    .00064

              E = --------- = ------- = .00008

                       8           8

 

                        TWA

              .00008 = ----

                        106

 

              TWA = 80 ppm

 

              The PEL for methyl styrene (from Appendix A.1) is 100 ppm and is preceded by the letter C, which identifies it as a "ceiling" concentration, not a TWA.  The AL, at one-half the PEL, would be 50 ppm, also a "ceiling" concentration.  Since the afternoon concentration, at .00015 = 150 ppm, exceeds both PEL and AL ceilings, both PEL and AL are exceeded, even though the TWA at 80 ppm is lower than the PEL.

 

9.14.         NOTE: This problem has been complicated by a change in nomenclature as used in the OSHA standards.  The organic chemical names "trifluoromonobromomethane" and "trifluorobromomethane" are synonyms.  OSHA PEL tables have dropped the "mono" from the name and Appendix A.1 lists the PEL for  "trifluorobromomethane."  Students should be advised to use this entry in solving this problem.

 

              (a)                                      Concentration           Duration

                     trifluorobromomethane                    .001                3 hrs

                     propane                                  .0005               8 hrs

                     phosgene                                 1 x 10-6             1/4 hr

 

              TWA    = .001 x 3 (106) = 375 ppm  (trifluorobromomethane)

                           8

 

              TWA    = .0005(8) (106) = 500 ppm  (propane)

                           8

 

              TWA = 1/10-6 x 1/4 (106) = .03125 ppm  (phosgene)

                           8

 

              Em = S Ci  =  375  +  500  + .03125

                     LI    1000    1000     .1

 

                         = .375 + .5 + .3125

 

              Em = 1.1875

 

              Since Em > 1, the mixture exceeds the OSHA PEL (and the AL, too).

 

              (b)    The given exposure levels of the trifluorobromomethane and propane (without any phosgene exposure) already exceed the AL (.375 + .5 = .875 > .5). To determine the allowable exposure to phosgene to keep the total mixture below the PEL, we subtract the other exposures from "1" to find the allowable time of concentration permissible for phosgene:

 

                     1 - [.375 + .5] = .125 allowed for phosgene

 

                     Time of exposure x concentration < .125

                           8 hrs x PEL (phosgene)

 

                     Time x 1/106 < .125

                       8 x .1/106

 

                     Time < .125 x 8 hrs x .1

 

                          < .1 hr = 6 min

 

              Therefore, to meet the OSHA PEL a total of 6 minutes exposure of phosgene (at one part per million) is permissible given the other contaminants.  This represents a decrease in exposure of 9 minutes (15 min. - 6 min. = 9 min.).

 

 

9.15.         Tube A provides greater precision.  Note that Tube A measures a more precise range (0.5 to 10 ppm) using the same number of pump strokes (5) that for Tube B will measure a much broader range (5 to 100 ppm).  Tube B would be better for gross concentrations, but for a precise measurement within its range Tube A is better.

              The PEL for nitrogen dioxide can be found in Appendix A.1 to be 5 ppm. Tube A provides better precision and has the capability of measuring concentrations both below and above 5 ppm.  Tube B would be better for much higher concentrations.

              The AL for nitrogen dioxide is 2.5 ppm (1/2 PEL).  Tube A again would be better for checking concentrations at close to the AL because it is more precise and its sensing range encompasses 2.5 ppm.  Tube B is barely able to detect concentrations at 2.5 ppm because its lower detection limit is 2 ppm, using 10 pump strokes.

 

9.16.                CO                         Iron Oxide                 Manganese

              Conc.  Length C x L         Conc.  Length C x L Conc. Length C x L

              10       2      20          1        2       2           1      2       2

              20       2      40          4        2       8           1      2       2

              25       1      25          2        1       2           0      1       0

              30       3     90           3        3       9          1      3      3

              Total         175          Total            21         Total            7

 

              TWA CO = 175/8 = 21.875 ppm

 

              TWA CO2 = 1000 ppm

 

              TWA Iron Oxide = 21/8 = 2.625 mg/m3

      

              TWA Manganese = 7/8 = .875 mg/m3

                                 

 

              Substance            PELs from Appen A.1

              CO                     50 ppm                  

              CO2                  5000 ppm                  

              Iron Oxide             10 mg/m3                 

              Manganese            (C)5 mg/m3                 

 

              Since the PEL for manganese is shown as a C (Ceiling) concentration, the ceiling observed during the shift must be used in the Em equivalent mixture calculation.  Thus, for the manganese term in the summation, the ratio is 1/5 for the ceiling concentration, not the TWA ratio of .875/5.

 

              Em = S Ci  = S TWA

                      Li      PEL

 

                 = 21.875   +      1000   +    2.625   +  ­ 1  

                      50           5000         10          5

 

                 = .4375 + .2 + .2625 + .2

 

              Em = 1.050

 

              Since Em = 1.050 > 1, the mixture exceeds the PEL.

 

9.17.         Most dangerous: asbestosis, silicosis

              Others: siderosis, stannosis, byssinosis, aluminosis

 

9.18.         Fibrosis is a more serious condition which includes the development of scar tissue in the lungs.

 

9.19.         Simple asphyxiants: methane, nitrogen, carbon dioxide

              Chemical asphyxiants: carbon monoxide, hydrogen cyanide

 

9.20.         (a) mutagens--substances that are harmful to chromosomes (species)

              (b) carcinogens--substances that are know to cause or are suspected to cause cancer

              (c) teratogens--substances that are harmful to the fetus

 

9.21.         At home, ingestion, skin contact, then inhalation are the order of most frequent occurrences of poisoning.  At work, the order is reversed.

 

9.22.         Vapors are gases that come from substances that are normally in a liquid or solid state.  Fumes are solid particles which are too fine to be considered as dust.  Fumes are usually formed by the resolidification of vapors from very hot processes such as welding.

 

9.23.         (a) zinc oxide fumes              .01 to  0.3 micrometers

              (b) tobacco smoke                        .01 to 0.4 micrometers

              (c) diameter of human hair               500 to 700 micrometers

              (d) bacteria                             .2 to 20 micrometers

 

9.24.         (a) TLV--"threshold limit value": that level of concentration to which the worker could be exposed during the entire workday without significant harm.

              (b) PEL--"permissible exposure level": prescribed by OSHA or other enforcement agency.  Many PELs are numerically the same as the corresponding TLV.

              (c) TWA--"time-weighted average": exposure level averaged over an 8 hour time period.

              (d) MAC--"maximum acceptable ceiling": PEL should never be exceeded.  TWA is not applicable when a MAC is set.  Substances for which a MAC applies are identified by "C" (ceiling) in the OSHA PEL tables.

              (e) STEL--"short-term exposure limit": STEL states a maximum concentration permitted for a specified duration.

              (f) AL--"action level": usually set at 1/2 of the PEL.

 

9.25.         (1) Smell--convenient but unreliable.

              (2) Examining technical literature to determine what industries might release what substances--good way to find some agents to check for.

              (3) Analyzing the processes in the plant to determine potential leaks to the atmosphere; this can be very effective if it is done thoroughly; a chemical engineer may need to be consulted.

 

 

9.26.         (1) Direct-reading instruments

              (2) Sampling and subsequent laboratory analysis

              (3) Dosimeters

 

9.27.         Methanol is a synonym for methyl alcohol.

                                                   Nitric        Sulfur     Total

              Period               Methanol          Oxide       Dioxide  (Mixture)

              Time                 Ti     Ci     CiTi     Ci   CiTi   Ci     CiTi  

                                                                                    

               8:00-10:00       2 hrs     50    100       5   10    0       0

              10:00-11:00       1 hr      150    150      10   10    1       1

              11:00- 1:00       2 hrs     100    200       5   10    1       2

               1:00- 4:00       3 hrs     200    600      10   30    1       3        

                Total           8 hrs           1050           60             6

 

              TWA           1050/8 = 131.25      60/8 = 7.5           6/8 = .75

 

              PEL             200                25                    5

 

              Ratio TWA/PEL 131.25/200 = .65625 

                                      7.5/25 = .3     

                                        .75/5 = .15

                                              1.10625  > 1.0; mixture exceeds the PEL. 

                     (Also exceeds the AL, of course)

      

9.28.         PEL for ethanol (ethyl alcohol) = 1000 ppm

              Since the PEL for ethanol (1000 ppm) is 5 times the PEL for methanol (200 ppm), and the new concentration (of ethyl alcohol) would be only double the old concentration (of methyl alcohol), the process change would help to reduce the health hazard.  The new concentration would have a smaller ratio to its PEL and would thus improve matters.  The advantage of this improvement could be shown numerically by recalculating the total equivalent mixture ratio sum.  (The result is a reduction from 1.10625 to 0.7125, which is less than 1 and thus within the PEL for mixtures.)

 

9.29.         OSHA recognizes both solvents as hazards.  Chlorobenzene is listed in Table A.1 as having a PEL (TWA) of 75 ppm.  Benzene is much worse, being recognized as a depressant on the central nervous system, an irritant, a systemic poison, and a carcinogen (in its role as a cause of leukemia).  In addition, benzene is a dangerous fire and explosion hazard.  So hazardous is benzene that OSHA has issued a separate standard for it (29 CFR 1910.1029) as a part of the "standards completion project."  In addition it is listed in Table A.2 as having a PEL (TWA) of 10 ppm.  If there are only two choices, and other factors are equal, chlorobenzene should be selected.

 

9.30.         Volume of room = 600 ft2 x 8 ft = 4800 ft3

 

                                          5 ft3

              Concentration (initial) = ------- = .001042 = 1042 ppm

                                         4800 ft3

 

              Assuming a steady dilution due to the open window, the average concentration for the 8-hour all-night period is:

 

              1042 + 500           1542

              --------------- = ------ = 771 ppm

                     2               2

 

              PEL for ethyl alcohol = 1000 ppm

              Since 771 ppm < 1000 ppm. PEL is not exceeded.  (The AL is exceeded.)

 

9.31.         With the hot oven adding an additional 25 ft3 of alcohol vapor to the room, the total would be 5 ft3 + 25 ft3 = 30 ft3.  Under these new conditions, six times as much vapor has been introduced into the apartment's air.  If it is assumed that the initial and average concentrations are also six times as great as in Exercise 9.30, then:

 

              Concentration initial = 6 x 1042 ppm = 6252 ppm

              Average concentration » 6 x 771 ppm = 4626 ppm

              Since 4626 ppm > 1000 ppm, PEL is exceeded.

 

9.32.                                           Range                     

                                  Tube 5H                     Tube 5M      

                            Lower         Upper         Lower         Upper  

              Percent       .05%          8.0%          .002%         .36%

              PPM           500           80000         20            3600

 

                     Tube 5M is more sensitive.

 

9.33.         Ceiling (MAC) concentration for hydrogen sulfide (H2S) is 20 ppm (from Appendix A.2 of the text).

              Four tubes in the table encompass the 20 ppm MAC.  They are 4H, 4M, 4L, and 4LL.  Tube 4LL covers the narrowest range (.25 ppm - 60 ppm).

 

9.34.         From Table A.1 of the text, the PEL (TWA) for isopropyl acetate is 250 ppm.  The AL = 1/2 PEL = 125 ppm

 

              Detector tube range: 0.05% to 0.75%

 

              converted to ppm:

                     Detector tube range: 500 ppm to 7500 ppm

 

              The detector tube is of insufficient sensitivity to be useful as a detector of concentrations near the PEL or AL.

 

                                                                                        

9.35.         1 micrometer = 10-6 meters; 1 cm = 10-2 meters; 1 cm = 10-4 micrometers

              Diameter in centimeters = 17 x 10-4  =  0.0017 cm

              Diameter in inches = .0017cm/2.54 cm/in = .00067 in.

              The particle would be classified as dust.

 

9.36.         Contaminant                Conc          PEL           AL

 

              Isopropyl ether            200           500           250

              Ethyl benzene              40           100           50

              Chlorobenzene              25           75           37.5

              Chlorobromomethane         50           200           100

 

              Taken separately none of the contaminants exceed either their respective PEL's or AL's.  When considered together, however, the following formula is used for mixtures:

 

              Em = (200/500) + (40/100) + (25/75) + (50/200)

                 = .4 + .4 + .33 + .25 = 1.38

 

              Since 1.38 > 1 and 1.38 > 0.5, the concentrations exceed both the PEL and the AL, respectively.

 

9.37.         On the surface it appears that the new solvent will help matters by reducing the solvent vapor release by 20%.  However, 20% is only a modest improvement, and a more knowledgeable assessment would include a comparison of the PELs for the two solvents under consideration.  The old solvent, Stoddard solvent, is listed in the OSHA list for air contaminant PELs as a TWA of 500 ppm (see Appendix A.1).  The new solvent, perchloroethylene is listed in Appendix A.1 with a reference to Appendix A.2. Earlier editions of the Appendix have recognized "perchloroehtylene" and "tetrachloroethylene" as synonyms. Tetrachloroethylene is found in Appendix A.2 to have a TWA PEL of 100 ppm and a MAC of 200 ppm.  Therefore perchloroethylene is much more tightly controlled as a more hazardous substance than Stoddard solvent.  The advantage of the modest reduction in solvent vapors is more than offset by the fact that the new solvent is much more dangerous, five times as dangerous as indicated by the ratio of PELs.  It would be more difficult to control the new solvent to levels within the PEL and AL.  The consultant should point this out to the process engineer and caution against making the process change.

 

 

9.38.                             Morning