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NIOSH Publication No. 2006-149:Preventing Asthma and Death from MDI Exposure
During Spray-on Truck Bed Liner and Related Applications
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September 2006
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BackgroundSpray-on polyurethane/polyurea products containing isocyanates such as MDI have been developed for a wide range of retail, commercial, and industrial uses to protect cement, wood, fiberglass, steel, and aluminum surfaces such as truck beds, trailers, boats, foundations, and decks. MDI, toluene diisocyanate (TDI), and the polyisocyanate products based on the diisocyanate hexamethylene diisocyanate (HDI) are the most commonly used diisocyanates in the polyurethane industry. Isocyanates are widely used in the manufacture of flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers. Isocyanates are increasingly used in the automobile industry, autobody repair, and building insulation materials. (See Appendix A for definitions and synonyms of MDI and information about its chemical structure.) Production and consumption data for the polyurethane industry in the United States and North America are available through the Alliance for the Polyurethanes Industry (API). Their publications End-Use Market Survey on the Polyurethane Industry [API 2003] and Socio-Economic Impact of Polyurethanes in the United States [API 2004a] provide the following facts:
Inspections by the Washington Industrial Safety and Health Administration (WISHA) of the Washington State Department of Labor and Industries at 13 spray-on truck bed lining businesses and a review of industrial insurance records found that workers are at risk of developing illnesses associated with diisocyanate exposure [Lofgren et al. 2003]. Seven of the 13 inspected worksites had MDI monomer air concentrations that were greater than the regulatory limit, resulting in regulatory citations. During their preparation of the report on inspections in Washington State, the authors contacted NIOSH and requested help with developing engineering controls and alerting affected employers and workers throughout the Nation. As a result, NIOSH began a study of the spray-on truck bed lining industry. NIOSH conducted walk-through surveys at spray-on truck bed liner facilities in Washington State, Colorado, Ohio, and Kentucky [NIOSH 2003a; Almaguer et al. 2004]. Six sampling surveys were conducted in Ohio and Kentucky. The results of the NIOSH sampling surveys are described later in this document. In 2003, Washington and Michigan actively began alerting the industry in their States of the hazards associated with spraying MDI in truck bed liner applications. In March 2003, WISHA issued a Hazard Alert warning of isocyanate exposures related to the spray-on truck bed lining industry [WISHA 2003]. The Michigan Occupational Safety and Health Act News described a fatality that occurred in Michigan during the application of an MDI-based spray-on bed liner to the interior of a van in February 2003 [MIOSHA 2003]. In December 2003, the Michigan Fatality and Control Evaluation (MIFACE) Program issued a report on the death, and the Michigan Occupational Safety and Health Administration (MIOSHA) issued an Alert in January 2004 [MIFACE 2003, MIOSHA 2004]. In February 2004, WISHA issued a Hazard Alert Update briefly discussing the Michigan death and the health hazards associated with exposure to isocyanates [WISHA 2004]. This Alert is intended to notify workers and employers in the truck
bed lining and related industries of the adverse health effects associated
with exposure to MDI during the application of spray-on truck bed
liners. The current Alert also provides preliminary recommendations
to reduce worker exposures to MDI during the spray-on bed liner process.
Spray-On Truck Bed Lining ProcessThe spray‑on truck bed lining process involves applying a protective polyurethane or polyurea coating to the bed of pickup trucks or other vehicles and surfaces in a manner similar to undercoating. Bed liners are applied as a two-part resin. Part A is an MDI-based
product; part B is usually a polyol or polyamine that reacts with the isocyanate to form a tough, resilient elastomeric surface coating.The MDI-based liners are applied to pickup truck beds and other surfaces to protect them from damage and to provide anonskid surface. The spray-on application process is usually done in a spray enclosure. The spray-on truck bed lining process is commonly performed in spray-on truck bed specialty shops, auto body centers, and auto dealerships (see Figure 1). NIOSH identified two spray-on processes commonly found in the industry [Heitbrink and Almaguer 2003]: one process applies truck bed liners at room temperature and pressures of approximately 50 pounds per square inch (low temperature/low pressure); a second process applies truck bed liners at temperatures above 165 °F and pressures of approximately 1,500 pounds per square inch (high temperature/high pressure). In both processes, the A and B components are pumped separately to the spray gun and mixed at the time of application. The worker uses a hand-held spray gun to apply the rapidly curing product onto the truck bed interior. The shape of the spray pattern is determined by the nozzle shape. To create a textured, nonslip surface on the bed, a small quantity of the coating is sprayed into the air, allowing the product to settle onto the truck bed. To obtain a bed liner thickness of 0.125–0.25 inches (a standard in the industry), approximately 50 pounds of the two-part resin (part A and part B) are sprayed onto the bed and inside walls of a typical pickup truck (see Figure 2). A third type of spray-on process that was not included in the NIOSH
sampling surveys is the cold-batch, pre-mix process. The information
contained in this Alert may apply to this process as well. During
this process, isocyanate/resin and catalyst materials are generally
mixed in small quantities (quarts or gallons) at room temperature
with a high-speed drill. Afterwards, the mixture is poured into a
hopper gun and applied at 30–60 pounds per square inch from
inside the truck bed. The chemicals used in the cold-batch operations
typically contain less MDI (less than 20%). However, the cold-batch
materials contain higher amounts of flammable solvents (toluene and
N-butyl Spray Applications Other Than Truck Bed LiningPolyurethane and polyurea coatings are marketed and used for truck trailers, house decks, walls, foundations and sports flooring, and they are likely to be used for other applications as well. In many cases, these applications use the same or similar chemicals, spray techniques, and equipment as the spray-on truck bed lining process. Because of these similarities, excessive exposure to MDI may occur during these related applications, resulting in risk to spray gun users and other nearby workers. Owners and managers of these operations should assess and sample as necessary as well as implement needed controls and work practices, including engineering controls, worksite-specific respiratory protection programs, chemical hazard training, administrative controls, and use of personal protective equipment for exposed workers as outlined in this Alert [Lofgren et al. 2003]. Health Effects Of IsocyanatesIsocyanates are the leading attributable chemical cause of occupational asthma in the United States and many other industrialized countries [Tarlo et al. 1997b]. Workers with asthma symptoms from isocyanate exposure often continue to have symptoms after exposures have been terminated. Affected workers often have to leave their jobs to prevent progression of respiratory symptoms.
The major route of work-related exposure to MDI is inhalation of the vapor or aerosol. Because the odor threshold for MDI is many times above the recommended exposure limit (REL), smell should never be relied on as an indication of exposure, nor should the absence of odor be used to indicate safety. MDI can be detected by odor only after dangerous concentrations exist, resulting in potential overexposure. Exposure may also occur through skin contact during the handling of liquid MDI-based products. Work-related exposure normally occurs during the spray application of MDI-based products. In 1996, NIOSH issued Preventing Asthma and Death from Isocyanate Exposure, which summarizes reported cases of disease and death following occupational exposure to diisocyanates and diisocyanate-based products [NIOSH 1996]. Irritation and Lung InjuryMDI and other isocyanates may irritate the mucous membranes of the eyes, upper and lower respiratory tracts, gastrointestinal tract, and skin [Swensson et al. 1955; Fisher 1967; Upjohn Company 1970; Lofgren et al. 2003]. Eye tearing, nose and throat irritation, and cough may occur [Littorin et al. 2000]. Respiratory irritation may progress to chronic upper and lower respiratory symptoms, although symptoms of local irritation do not reliably indicate chronic respiratory conditions [Wang and Petsonk 2004]. Acute respiratory distress syndrome or reactive airways dysfunction syndrome may also result from short-term high exposures [Tarlo et al. 1997b; Banks 1998]. Respiratory Sensitization Isocyanates can sensitize workers, making them subject to severe asthma attacks if they are exposed again, even when concentrations are continuously below the NIOSH REL [NIOSH 1973, 1978; Banks 1998]. Skin exposures may be associated with the onset of respiratory symptoms [Petsonk et al. 2000]. Respiratory disorders associated with isocyanate exposure include asthma and hypersensitivity pneumonitis [Baur et al. 1984; Baur 1995]. Sensitization may result from a single episode of overexposure or intermittent exposures at low concentrations. Once a worker is sensitized, even low concentrations may trigger symptoms such as wheezing, chest tightness, shortness of breath, and cough. Persons with chronic hypersensitivity pneumonitis may also experience fatigue and weight loss. These symptoms may begin immediately or may be delayed for up to 8 hours after exposure. Death from severe asthma in sensitized subjects has been reported [Fabbri et al. 1988; MIFACE 2003]. CarcinogenicityIsocyanates may cause cancer in animals; however, evidence is insufficient to describe the carcinogenic potential of MDI in humans. Data from recent studies show that methylene dianiline (MDA), a known animal carcinogen and the principal metabolite of MDI monomer, is found in the blood of MDI-exposed rats and in the urine of humans exposed to a mixture of polymeric MDI and MDI monomer [NIOSH 1986; Sepai et al. 1995]. Another study found that a commercial grade of MDI (45% MDI monomer by weight) induced chromosome aberrations in human blood lymphocyte cultures after a 24-hour treatment [Mäki-Paakkenen and Norppa 1987]. NIOSH recommends that work-related exposure to MDI be minimized because of the potential for respiratory sensitization and the potential carcinogenicity of the metabolite MDA [NIOSH 1986]. Current Exposure LimitsOccupational exposure standards for MDI are based on respiratory irritation and sensitization. The available human evidence is insufficient to describe the carcinogenic potential of MDI [NIOSH 1989]. The evolution of the occupational exposure standards for isocyanates is discussed in the literature review Polyisocyanates in Occupational Environments: A Critical Review of Exposure Limits and Metrics [Bello et al. 2004]. The isocyanate product frequently used in bed-liner formulations consists of varying amounts of MDI monomer and higher molecular weight species. Long-term aerosol inhalation studies suggest that monomeric MDI and polymeric MDI, which typically contain 50% monomer, have a similar response in rat lungs [Feron et al. 2001]. Mandatory and recommended limits have been established for MDI monomer, as discussed below. However, no recommended or regulatory limit exists for higher molecular weight species at this time. Therefore, regardless of the relative amount of MDI monomer present, owners and workers are encouraged to adhere to the control methods outlined in this Alert whenever MDI aerosols may be generated through a spray-on bed-lining operation. NIOSHNIOSH recommends that MDI monomer exposure be limited to 0.05 milligram
per cubic meter of air (mg/m3) or 0.005 part per million parts of
air (0.005 ppm) as a time-weighted average (TWA) for up to a 10-hour
workday during a 40-hour workweek, with a ceiling limit of 0.2 mg/m3
(0.02 ppm) The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for MDI monomer is 0.2 mg/m3 as a ceiling limit (0.02 ppm) [29 CFR* 1910.1000 (a)(1)]. Workplace Exposure AssessmentsWashington State In response to health concerns, Washington Industrial Safety and Health Administration (WISHA) inspectors conducted exposure assessments at 13 spray-on bedliner establishments [Lofgren et al. 2003]. Airborne concentrations of MDI monomer during the 10- to 20-minute application process varied between shops and ranged from 0.045 to 6.5 mg/m3. In 7 of the 13 shops, airborne concentrations of MDI monomer exceeded the State and OSHA ceiling limit of 0.2 mg/m3. The method used for most samples consisted of an open-faced cassette having a filter treated with 1-(2-pyridyl) piperazine. WISHA concluded that conditions contributing to excess exposure included inadequate exhaust and make-up air, clogged ventilation filters, and a lack of training and awareness of the hazard. Workers who applied spray used either a supplied-air respirator or an air-purifying respirator with filter cartridge. Companies were cited for deficient respirators, inadequate respirator training programs, and lack of respirator fit-testing and engineering controls. Seven of the worksites with overexposure to MDI had one or more serious violations related to respirator use. In addition, one establishment using a bedliner product containing a flammable solvent received a violation for the presence of sources of ignition in the spray area. NIOSH The following summarizes MDI monomer exposure assessments from NIOSH surveys conducted at six spray-on truck bed liner sites. These exposure assessment sites included three surveys at low-temperature/low-pressure operations and three surveys at high-temperature/high-pressure operations. Samples were collected in the spray enclosures during the bedliner application process, in truck preparation areas, in the office areas, and outdoors as close as practicable to the spray enclosure exhaust grill. Sampling was done for the duration of the process, which ranged from 16 to 43 minutes in the spray enclosure. Longer- duration sampling was done in areas outside the spray enclosure. The air samples were collected and analyzed using NIOSH Method 5525 [isocyanates, total (MAP)], which uses 1-(9-anthracenylmethyl)-piperazine (MAP) as the derivatizing reagent [NIOSH 2003b]. In accordance with the recommendations in NIOSH Method 5525 for sampling MDI aerosols, an impinger with MAP reagent solution followed by a MAP reagent-coated filter was used for collecting the air sample. The laboratory analysis of samples used high-performance liquid chromotography with ultraviolet absorbance/fluorescence detection. Spray EnclosureThe data from these six surveys show that the greatest risk for
exposure occurs, as expected, in the spray enclosure. Airborne concentrations
of MDI monomer were up to 27 times the NIOSH REL of 0.2 mg/m3 as
a 10-minute ceiling concentration in the spray enclosure during the
spray-on process. The geometric mean MDI monomer concentration in
the spray enclosures at the low-temperature/low-pressure process
was 0.99 mg/m3, or approximately 5 times the NIOSH REL. The geometric
mean MDI monomer concentration in the spray enclosures at the high- After the spray application process, post-spray air samples were collected inside the spray enclosure. Eight of 12 post-spray samples showed low concentrations of MDI monomer; 4 of the 12 samples had nondetectable concentrations. These samples were typically 15- to 30-minute samples and ranged from below the limit of detection to 0.08 mg/m3. These results are averaged over the duration of the sample; concentrations immediately after spray application are expected to be higher and may require respiratory protection when re-entering the booth (usually to remove the vehicle) (see Recommendations). Truck Preparation AreaAirborne MDI monomer in the truck preparation area averaged 0.56% of that in the spray enclosure. Eight of the 12 samples taken in the truck preparation area were below the limit of detection. The four samples above the limit of detection had concentrations that ranged from 0.0057 to 0.022 mg/m3. Unlike spray gun users, the workers in the truck preparation areas did not wear respirators designed to protect from exposure to MDI. The concentrations in the truck preparation area were below the NIOSH REL. However, detecting any MDI in the truck preparation area indicates that the spray enclosure was not under negative pressure as recommended. Because of the potential for worker sensitization to MDI, the spray enclosure should be maintained under a negative pressure to minimize the possibility that MDI monomer will escape from the spray enclosure to the truck preparation area or other adjacent work areas, and prevent worker sensitization. Office AreaIn five of the six surveys, airborne MDI monomer in the office/lobby areas was below the limit of detection. Trace concentrations of MDI monomer (below the limit of quantitation) were detected in the office/lobby area of one shop. Again, this finding indicates that the spray enclosure was not under negative pressure as recommended, thereby presenting the potential for exposure to the office occupants. Placing the office/lobby areas as far as possible from the spray enclosure and exhaust areas minimizes possible exposure to MDI in these areas. Exhaust AreaFive of eleven outdoor samples for MDI monomer taken near the spray enclosure exhaust had concentrations greater than the limit of detection; the highest was 0.41 mg/m3. These data indicate a potential for exposure to MDI in the exhaust area of the building, requiring restrictions as addressed in the Recommendations. Observations at the surveyed worksites suggest effective exhaust ventilation may have reduced MDI monomer concentrations in the spray enclosure during spray applications [Almaguer et al. 2004]. Only one site had an exhaust system designed to effectively capture contaiminants in the spray enclosure; at this site, airborne MDI was reduced to concentrations near the NIOSH REL. Airborne concentrations at 5 other sites with general exhaust ventilation were 3 to 27 times the NIOSH REL. Case ReportsThe following case reports highlight examples of isocyanate-induced asthma, other respiratory disease, and death. Case 1 — Spray-on Truck Bed Lining (Fatal Asthma)A 45-year-old male worker with 1 year of tenure died from an acute asthma attack after spraying an MDI-based bed liner onto the floor and sides of a cargo van interior. The worker was wearing a half-mask, supplied-air respirator as well as latex gloves and coveralls. The spray area was defined only by “two curtains that could be pulled together to enclose the area and limit product overspray into the general shop area.” The room had no local exhaust ventilation. Room ventilation during the spray-on bedliner application was provided by raising the overhead door a few feet, opening the door near the rust-proofing area, and placing a box fan at this door to provide air circulation. After completing the job, the worker turned off the mixer for the spray-liner components (MDI and polyether polyol). He disconnected his airline from the respirator and walked around to the front of the building, where a coworker found him in acute respiratory distress. The coworker took him to a nearby urgent care facility where he developed cardiac arrest. He did not respond to cardiopulmonary resuscitation. An ambulance took the worker to the local hospital emergency room where he was declared dead. After an autopsy, the county medical examiner stated that the worker had died of an “acute asthmatic reaction due to inhalation of chemicals.” In the past, the worker had tried to spray bed liners when customers and coworkers were not present because of the strong odors associated with the product. After the fatality, coworkers informed the owner that the victim said he had difficulty breathing after applying the bed liners and that he had used an inhaler. This fatality may have been caused by MDI sensitization. The spray area was enclosed with a curtain (not a permanent enclosure) and had no dedicated exhaust ventilation. The worker used a spray-gun and a half-mask, supplied-air respirator. Furthermore, the MIFACE report indicates that the worker told coworkers that he had had previous breathing difficulties after spraying bed liners and that he had used an inhaler in the past. This suggests that MDI sensitization probably occurred in the past and played a significant part in the fatality. The information reinforces the need for strict adherence to the recommendations in this Alert. Whether the worker knew that his past breathing problems were associated with his exposures at work was unclear, since he did not report them to the owner. No exposure assessment data are available for this fatality [MIFACE 2003; MIOSHA 2004]. Case 2—Spray-on Truck Bed Lining (Asthma)A 29-year-old male ex-smoker who worked spraying truck bed liners arrived at a hospital emergency room with complaints of chest discomfort and wheezing. He reported having been exposed to “fumes” generated during the application of MDI-based spray-on truck bed liners. He reported increasingly frequent episodes of shortness of breath and wheezing associated with exposure to isocyanates during 8 months of work at the truck bed lining company. The worker was diagnosed with asthma, treated with inhaled bronchodilators and intravenous steriods, and advised to see a pulmonologist. The emergency room record indicated that the physician failed to identify the isocyanate exposure reported by the worker as a possible etiology of the worker’s asthma [Bonauto and Lofgren 2004]. Case 3—Spray-on Truck Bed Lining (Asthma)A 30-year-old man developed rhinitis, a cough, wheezing, and shortness of breath 4 months after starting work spraying truck bed liners. On one occasion, the worker reported to the emergency room but was not diagnosed with asthma. Symptoms persisted with daily episodes of shortness of breath, wheezing, and nausea. These symptoms occurred at midday after four to five bed liner applications. After 4 months of symptoms, which culminated in hospitalization for respiratory distress, the worker was diagnosed with work-related asthma from exposure to MDI. After hospitalization, the worker was documented to have nonspecific bronchial hyperreactivity by methacholine challenge testing. No inhalation challenge with MDI or workplace challenge testing was ever performed. The worker was removed from the workplace. One year later, the worker was employed elsewhere as a manual laborer. He still had symptomatic asthma and was maintained on bronchodilators and inhaled steroids [Bonauto and Lofgren 2004]. Case 4—Spray-on Truck Bed Lining (Asthma)A 22-year-old worker who used a spray gun was employed in the truck bed lining industry for 18 months. He developed a runny nose and nasal congestion that occurred during the workweek but improved over the weekend. Increased breathing difficulty on exertion restricted his daily activities. The worker underwent a medical evaluation that included spirometry before and after the administration of bronchodilators. He was documented to have a reversible airflow limitation and was diagnosed with asthma. No workplace challenge testing was performed. The material safety data sheets (MSDSs) provided to the medical personnel revealed that the spray-on bed liner material consisted of 50% to 60% MDI monomer and 5% to 20% diisooctyl phthalate. The worker was removed from the workplace. A year and a half after medical removal from the workplace, the affected worker was still unemployed. He continued to have symptomatic asthma and was maintained on bronchodilators and steroid inhalers [Bonauto and Lofgren 2004]. ConclusionsThe cases described in this document reveal the potentially serious nature of respiratory disease resulting from exposures to MDI in the spray-on truck bed liner industry. Exposures may increase the risk of serious respiratory disease, respiratory sensitization, and death. MDI concentrations generated by the spray-on application of truck bed liners at the NIOSH exposure assessment sites routinely exceeded the NIOSH and OSHA ceiling limits and varied throughout the process with unpredictable, rapid increases in airborne concentrations. On the basis of these findings, NIOSH concludes that only a full-facepiece, supplied-air respirator provides the necessary protection during MDI spray operations. RecommendationsManufacturers and distributors of spray-on polyurethane/polyurea products containing MDI and other isocyanates should work together to assess and determine the best controls for the spray-on bed liner process. The ultimate goal is to establish procedures and develop controls (such as proper ventilation) to minimize MDI concentrations within the spray enclosures. These procedures and controls—together with respirator use, a written respiratory protection program, and ongoing worker training—will reduce the risk for worker exposures during the spray-on process. General Responsibilities for Shop Owners and Workers to Prevent MDI Exposures
General Responsibilities of Manufacturers, Distributors, and Franchisers of Spray-on Chemicals and EquipmentProvide safety and health information to users of your chemicals and equipment. Include information about design of spray enclosures, engineering controls, safe work practices, and the hazards of exposure. These two references are excellent examples of useful information:
Develop, publish, and distribute additional safety and health resources to help workers using spray-on MDI products. Detailed RecommendationsThe following sections provide detailed recommendations for this industry, including further guidance about the choice of respirators and appropriate ventilation parameters. Product SubstitutionWhen feasible, substitute a less hazardous material for MDI and other isocyanates. NIOSH policy is always to recommend using a less toxic substitute if available. Water-borne acrylic coatings, polysulfide rubber coating, and epoxy are other chemicals that have been used to make truck bed liners. Drop-in truck bed liners are also commercially available. NIOSH cannot address the quality or performance and has not addressed the safety of these products. In addition, using substitute chemical processes or products may have advantages and disadvantages, including safety and health issues that are not addressed in this Alert. Equipment/Formulation Modification
These design, process, and formulation changes could reduce airborne MDI, resulting in reduced worker exposures. They would also place less financial burden on retail owners and operators in controlling airborne contaminants during the spray process. Furthermore, less overspray would produce less waste and provide further economic benefit for the retail owner. Unverified evidence from a spray-on bed liner company suggests that using lower pressures (10 pounds per square inch) may reduce airborne MDI concentrations and thus lower the exposure. Spray Enclosure and VentilationVentilation design (see Appendix B)
Work practicesSpray gun users should be trained to make their work practices compatible with the control concepts of the ventilation system:
Ventilation system capabilities
Ventilation maintenance
Spraying in Enclosed Areas
Worker Isolation
Exposure Monitoring
Additional assistance about managing this or other hazards can be obtained from the free, onsite OSHA consultation service in your State. For information about the OSHA Consultation Program, visit www.osha.gov/dcsp/smallbusiness/consult.html or call 1–800–321–OSHA (1–800–321–6742). Respiratory ProtectionTypically, respirators should not be used as the primary control for routine operations except during situations such as implementation of engineering controls, some short-duration maintenance procedures, and emergencies. NIOSH exposure assessment data show that the engineering controls at the NIOSH survey sites did not reduce MDI concentrations below the occupational criteria, even at the sites with the best ventilation controls [Almaguer et al. 2004]. Airborne MDI monomer concentrations in the spray enclosures during the spray-on application process routinely exceed both the NIOSH 10-minute ceiling limit (0.2 mg/m3) and the OSHA PEL as a 15-minute ceiling concentration (0.2 mg/m3). Therefore, NIOSH recommends the following respiratory protection for the spray-on truck bed liner industry. (See Appendix C for more information about respirators and respiratory protection.) Use supplied-air respirators when spraying MDI
Use air-purifying respirators for entry into the enclosure after spraying
Develop a respiratory protection program
The following links provide additional guidance for developing written respiratory protection programs:
Personal Protective ClothingWhen spraying MDI-based products or during entry immediately after spraying, wear protective clothing such as hooded coveralls, chemical-resistant gloves, and footwear to protect the skin of the face, scalp, and neck areas from MDI aerosol as recommended in the publications Quick Selection Guide to Chemical Protective Clothing [Forsberg and Mansdorf 2003] and PMDI User Guidelines for Protective Clothing Selection [API 2002] (see Figure 3). Worker and Employer Education
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Figure 1. MDI Monomer |
An isocyanate is any compound that contains the -NCO functional group. A functional group is any group of atoms that represents a potential reaction site in an organic compound. An isocyanate thus has a nitrogen (N), carbon (C), and oxygen (O) bonded together in such a way as to create a reactive site within the molecule. In this document, the term diisocyanate refers to a chemical compound that contains two isocyanate groups (NCO) per molecule. When specifically referring to the diisocyanate methylenebis(phenyl isocyanate), the term MDI monomer will be used. The MDI monomer is depicted in Figure 1. The term MDI refers to a mixture containing any combination of MDI monomer, MDI prepolymer, or polymeric MDI.
The spray-on truck bed liner industry uses MDI-based products as one component of a two component spray-on process. Component A typically contains a mixture of MDI monomer(s) and modified MDI. All have reactive isocyanate groups present and should be considered possible health hazards.
1,1-Methylenebis(4-isocyanatobenzene)
4,4’-Diisocyanatodiphenylmethane
4,4’-Diphenylmethane diisocyanate
4,4’-Methylenebis(phenyl isocyanate)
4,4’-Methylenediphenyl diisocyanate
Bis(1,4-isocyanatophenyl)methane
Bis(4-isocyanatophenyl)methane
Diphenylmethane 4,4’-diisocyanate
Diphenylmethane diisocyanate
Methylenebis(4-isocyanatobenzene)
Methylenebis(4-phenylene isocyanate)
Methylenebis(phenyl isocyanate)
Methylene-di-p-phenylene isocyanate
Methylene di(phenylene isocyanate)
Methylene bisphenyl isocyanate (Chemical name used in OSHA documents.)
Sources: Lewis [1993], NIOSH [1995], Sax and Lewis [1987].
Table 1. CAS numbers associated with MDI* |
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CAS number |
CAS preferred name |
Description/ |
101–68–8 |
benzene, 1,1’-methylenebis[4-isocyanato- |
4,4’-MDI isomer, pure MDI |
5873–54–1 |
benzene, 1-isocyanato-2-[(4-isocyanatophenyl) methyl]- |
2,4’-MDI isomer |
2536–05–2 |
benzene, 1,1’-methylenebis[2-isocyanato- |
2,2’-MDI isomer |
26447–40–5 |
benzene, 1,1’-methylenebis[isocyanato- |
MDI (generic), mixture of isomers |
9016–87–9 |
isocyanic acid, |
PMDI, polymeric MDI (generic), mixture of chemical homologues made from the phosgenation of the reaction product of aniline and formaldehyde |
25686–28–6 |
benzene, 1,1’-methylenebis[4-isocyanato-, homopolymer |
Main components of polymeric MDI, mixture of chemical homologues derived from the 4,4’-MDI isomer |
17589–24–1 |
1,3-diazetidine-2,4-dione, 1,3-bis[4- |
4,4’-MDI dimer, self-reaction product |
31107–36–5 |
1,3-diazetidin-2-one, 1,3-bis[4-[(4- |
Uretonimine of 4,4’-MDI, a modified MDI (variant) made from self-reaction of 4,4’-MDI at high temperatures |
39310–05–9 |
benzene, 1,1’-methylenebis[isocyanato-, homopolymer |
Generic polymeric MDI, mixture of chemical homologues derived from the mixture of MDI isomers |
Source:
Allport et al. [2003]. |
Table 2. CAS numbers associated with specific MDI products† |
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Company |
CAS number |
Description |
The Dow Chemical |
26447–40–5 |
5 MDI products support the TBL business. All but one contains MDI prepolymers, which generally do call out the MDI prepolymer CAS number on the MSDS. |
Bayer MaterialScience |
39420–98–9 |
Bayer systems that are sold into the TBL industry are identified as Baytec SPR 085A and Baytec SPR 092A. Component A of each of these systems contains the MDI-based isocyanate. |
Rhino Lining |
26447–40–5 101–68–8 9016–87–9 |
The first two CAS numbers are for commercial Tuff Stuff A Side. The last CAS number is for PMDI (Durabond A Side) |
Line-X Corporation |
26447–40–5 |
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Huntsman Polyurethanes |
101–68–8 101–68–8 26447–40–5 101–68–8 101–68–8 101–68–8 |
MDI product name/Chemical name(s) RUBINATE® 8001/ RUBINATE® 1209/ RUBINATE® 9465/ RUBINATE® 9495/ RUBINATE® 9009/ SUPRASEC® 9537/ |
Source: API |
This Appendix contains information about spray enclosure and ventilation design, including how to determine the number of air changes per hour and calculate the minimum required purge time.
When substitution is not feasible, engineering controls should be the primary method for reducing airborne isocyanates in the workplace. Spray enclosures should incorporate exhaust ventilation systems designed to contain, capture and remove vapors and particulates. It is generally advisable to minimize the size and volume of the spray area while seeking to increase the exhaust capacity from the spray area. General design concepts and operating considerations for the ventilation control of occupational exposures may be found in the most recent edition of Industrial Ventilation: A Manual of Recommended Practice, published by the American Conference of Governmental Industrial Hygienists (ACGIH) [ACGIH 2004b].
The design and operation of a ventilated spray enclosure for MDI-based spray-on bed liners should include the following four parameters with the aim of containing and minimizing exposure to MDI and maintaining exposure to MDI monomer below the NIOSH 10-minute ceiling limit and OSHA 15-minute ceiling limit of 0.2 mg/m3:
This appendix contains additional information about full-facepiece, supplied-air respirators and a respiratory protection program.
Supplied-Air RespiratorsMany issues pertaining to this industry led to the selection of the full-facepiece, supplied-air respirator as the most appropriate respirator during the spray-on process. These reasons include the following:
A complete respiratory protection program as required by 29 CFR 1910.134 (c) (1) (i) through 1910.134 (c) (1) (ix) shall include the following:
Appropriate management is a critical part of an effective respiratory protection program. Therefore, the program should be evaluated regularly as required by 1910.134 (c) (1) and administered by a qualified program administrator as required by 1910.134 (c) (3). Workers using supplied-air respirators must follow the manufacturer’s instructions on how to maintain and verify the specified minimum air pressure for the respirator.
Surveillance Guidelines for State Health Departments
State health departments should encourage health-care professionals to report back all the diagnosed or suspected cases of asthma that are caused or exacerbated by workplace exposures or conditions. Reported cases should include asthma caused by sensitizers or irritants and should include cases of reactive airways dysfunction syndrome.
The surveillance case definition requires
Asthma is a chronic condition characterized by inflammation of the tracheobronchial tree associated with increased airways responsiveness to a variety of stimuli. Symptoms of asthma include episodic wheezing, chest tightness, cough, and dyspnea, or recurrent attacks of bronchitis with cough and sputum production. The primary physiological manifestation of airways hyperresponsiveness is variable or reversible airflow obstruction. It is commonly demonstrated by significant changes in the forced expiratory volume in 1 second (FEV1) or peak expiratory flow rate. Airflow changes can occur spontaneously, with treatment, with a precipitating exposure, or with diagnostic maneuvers such as nonspecific inhalation challenge.
Patterns of association can vary and include the following:
Work-related changes in medication requirements can accompany these symptom patterns.
Contact Information for Selected States
The following States have surveillance systems for work-related asthma:
California Department of Health Services
Occupational Health Branch
850 Marina Bay Parkway
Building P, 3rd Floor
Richmond, CA 94804–6404
510–620–5757
www.dhs.ca.gov/ohb/Default.htm
CAL/OSHA Consultation Service
Department of Industrial Relations
2424 Arden Way, Suite 485
Sacramento, California 95825
916–263–5765
www.dir.ca.gov/DOSH/consultation.html
State of Connecticut Department of
Public Health
410 Capitol Avenue, Mail Stop: 11 OSP
P.O. Box 340308
Hartford, CT 06134–0308
860–509–7744
www.dph.state.ct.us/BRS/EOHA/HPEEOH.html
Connecticut Department of Labor
Division of Occupational Safety and Health
38 Wolcott Hill Road
Wethersfield, CT 06109
860–566–4550
www.ctdol.state.ct.us/osha/osha.htm
Massachusetts Department of
Public Health
Occupational Health Surveillance Program
250 Washington Street, 6th Floor
Boston, MA 02108
617–624–5632
www.mass.gov/dph/bhsre/ohsp/ohsp.htm
MA Division of Occupational Safety
On-site Consultation Program
Department of Labor and
Workforce Development
1001 Watertown Street
West Newton, MA 02465
617–969–7177
www.mass.gov/dos/consult/index.htm
Michigan Department of Labor and
Economic Growth
Michigan Occupational Safety and Health
Administration (MIOSHA)
Consultation, Education, and
Training Division
7150 Harris Drive
P.O. Box 30659
Lansing, MI 48909–8149
517–322–1809
www.michigan.gov/cis/0,1607,7-154-11407---,00.html
Michigan State University
Department of Medicine
Occupational and Environmental Medicine
117 West Fee Hall
East Lansing, MI 48824–1315
517–432–1008
www.oem.msu.edu
New Jersey Department of Health
and Senior Services
Occupational Health Surveillance Program
P.O. 360, Room 701
Trenton, NJ 08625–0360
609–984–1863
www.nj.gov/health/eoh/survweb
NJ Department of Health and Senior Services
Public Employees Occupational Safety
and Health Consultation Project
P.O. Box 360
Trenton, NJ 08625–0386
609–984–1863
www.state.nj.us/health/eoh/peoshweb/peoshcon.htm
New Jersey Department of Labor
and Workforce Development
Division of Public Safety and Occupational
Safety and Health
P.O. Box 953, Trenton, NJ 08625
609–984–0785
www.state.nj.us/labor/lsse/lsonsite.html
State of New York Department
of Health
Center for Environmental Health
Bureau of Occupational Health
Flanigan Square
547 River Street, Room 230
Troy, New York 12180–2216
518–402–7900
www.health.state.ny.us/nysdoh/boh/
homeoccu.htm
New York State Department
of Labor
Division of Safety and Health
Onsite Consultation Program
State Office Campus, Bldg. 12, RM 168
Albany, New York 12240
518–457–2238
www.labor.state.ny.us/
Washington State Department of Labor
and Industries
Safety and Health Assessment and
Research for Prevention (SHARP) Program
P.O. Box 44330
Olympia, WA 98504–4330
888–667–4277
www.lni.wa.gov/Safety/Research/default.asp
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Telephone: 1–800–35–NIOSH (1–800–356–4674)
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or visit the NIOSH Web site at www.cdc.gov/niosh
DHHS (NIOSH) Publication Number 2006–149
September 2006