Document km6gDN1ByXKgMN0w2dOB78rzB

nose and throat m concentrations higher than 200 ppm Workmen exposed to about 100 ppm complained of headache and nausea but a tolerance developed dunng the working week Repeated or prolonged skm contact may cause drying of the skm with primary irritation resulting Prolonged or repeated contact with the skin should be avoided Methyl isobutyl ketone should be handled only in areas having adequate ventilation Methyl mercaptan (methyl sulfide) is the hydrogen sulfide ester of methanol Since it is readily hydrolyzed to the parent compounds, it has practically the same toxicity, both quali tatively and quantitatively, as hydrogen sulfide Methylcydohexane is similar m its effects to cyclohexane although it is slightly less toxic and has a lower vapor pressure Methylcyclohexanone seems to be somewhat less toxic than cyclohexanone, but the differ ences are not enough to be of practical im portance and the two substances are alike in their quahtabve effects Methylene chloride (dichloromethane) is one of the least toxic of the chlorinated hydro carbons However, because of its low boiling point, high concentrations of the vapor can be easily developed Its action is usually simply narcotic, although, when inhaled in high con centration, it is capable of producing liver damage Mica is a silicate mineral extensively mined for its high value as an electrical insulator and for a wide variety of other uses There is con siderable evidence that people working under excessive exposure to its dust suffer from a disabling pneumoconiosis See the discus sions in Chapter 37, "Industrial Hygiene " Molybdenum is considered an essenbal trace element m plants and possibly m mammals Its health hazard is described as moderate to low There is no evidence of acute or chronic industrial poisoning Pathological findings from animal experiments have been limited to such effects as bronchial and alveolar irritation with moderate fatty changes in liver and kidneys N Naphtha (coal tar) is mainly a mixture of toluene and xylene and should be treated like those compounds Naphtha (petroleum) is a rather indefinite term for any one of a number of solvent mix tures derived from petroleum oil One should define it more carefully before attempting to assess the hazard Naphthalene is a volable solid Vapors, given off when naphthalene is heated, form explosive mixtures with air Reports m the literature indicate that the mhalabon of naph thalene vapors may cause headache, loss of appebte, nausea, and kidney damage Ingesbon of naphthalene in relabvely large amounts has reportedly caused severe hemolybc anemia and hemoglobinuria A hypersuscepbbihty, probably genebcally based, is recognized Contact deimabbs may result from primary untabon or allergic hypersensibvity, or both Eye untabon may result from exposure to naphthalene vapor Prolonged exposure to high concentrabons of vapor can produce opacity of lens Opbcal neunbs and injuries to the cornea have also been reported The threshold limit value of 10 parts per million is recommended as a threshold limit to prevent ocular effects, but possibly not blood changes in hypersuscepbble individuals Naphthalene is not a senous industrial hazard providing that ordinary precaubons are observed to prevent contact with molten ma terial or excessive exposure to dust or high vapor concenbabons Nickel. In spite of its relabvely high toxicity, industrial experience with nickel has been good However, an increase in nasal, sinus and lung cancer has been noted in workers employed m nickel refineries The specific carcinogenic agent is still not defined and is the subject of conbnumg research The long-range carcinogenic potential should be re membered for all nickel compounds Dermabbs, or "nickel itch," is common among nickel platers It appears to have two components, a simple dermatitis localized to the area of contact and chronic eczema or 1157