4. Health Considerations

Acute Hazards

MDI and products containing unreacted MDI are potentially hazardous materials. Therefore, a thorough knowledge of potential dangers, with strict adherence to recommended safety practices, is essential before MDI products are handled, stored, or used. Workers must be properly instructed and supervised in the handling of MDI products. Limits have been established for allowable MDI vapor concentrations in the work environment.

MDI can be potentially hazardous in liquid, vapor, mist (aerosol), or dust form. Aerosols are airborne droplets and are present anywhere MDI is sprayed. Aerosols may also be formed when MDI is heated, such as melting pure
MDI for certain applications, and allowed to cool in the ambient air. These droplets may present a risk even at room temperature. A dust hazard may arise whenever MDI is absorbed on finely divided materials. If vapors, mists, or dusts are inhaled, MDI can cause respiratory symptoms similar to those caused by other isocyanates.

Some individuals may develop an allergic respiratory reaction (sensitization) to these MDI exposures. Sensitized individuals may thereafter be affected by very low concentrations. After serious vapor overexposure, pulmonary
edema can occur. Once sensitized, workers should be excluded from further exposure.

Exposure limits have been established by regulatory agencies and industry groups for MDI. The odor threshold of MDI is approximately 0.2-0.4 ppm; consequently, odor does not provide sufficient warning of overexposure. Table 4 identifies some of the current regulatory limits in effect. Permissible exposure limits (PELs) and ceiling limits should be sufficiently low to prevent sensitization in individuals. However, allergic reactions may occur in sensitized individuals at concentrations well below these values. MDI can produce local irritation upon contact with the skin, upper respiratory tract (nose, throat, and lungs), eyes, and mucous membranes.

Table 4. Regional exposure limits for MDI vapors.

Country	Agencies and Groups	Exposure Limits	ppm	mg/m3	Notes
Canada
Alberta		TLV	0.005	0.051	8 hrs TWA
British Columbia		TLV	0.005	0.051	8 hrs TWA
		PEL	0.01	0.1	Ceiling Limit
Ontario		TLV	0.005	0.051	8 hrs TWA
Québec		TLV	0.005	0.051	8 hrs TWA
U.S.A.	ACGIH	TLV	0.005	0.050	8 hrs TWA
	OSHA	PEL	0.02	0.2	Ceiling Limit
These values are subject to change and are given here only as examples of present limits. ACGIH - American Conference of Governmental Industrial Hygienists PEL - Permissible Exposure Limit Ceiling Limit - Concentration that should not be exceeded STEL - Short Term Exposure Limit (15 min exposure) TWA - Time Weighted Average TLV-Threshold Limit Value OEL- Occupational Exposure Limit WEL - Workplace Exposure Limit OSHA - Occupational Safety and Health Administration

Effects on the Respiratory System

Concentrations above the occupational exposure limit (OEL) of MDI vapor, aerosol, or dust may irritate the mucous membranes of the nose, throat, and lungs. It may cause throat dryness and tightness in the chest and breathing difficulties. Overexposure symptoms may be delayed. Allergic reactions can appear in susceptible persons. The health of all personnel coming into contact with MDI should be regularly monitored.

The inhalation LC50 (aerosol-4 hours rat) has been determined to be approximately 180 mg/m3 (MMDI) and 490 mg/m3 (PMDI). The MDI vapor concentration in a saturated atmosphere (13 ppb) is approximately 4,000 times lower than the LC50. No mortality in rats was observed at this concentration.

Effects on Eyes

Direct eye contact with MDI products may produce watering, irritation, and inflammation of mucous membranes. Discharge may result.

Effects on Skin

Skin contact with MDI may result in irritation and a mild tanning reaction, depending on the amount and length of contact. Direct contact may produce skin sensitization, contact dermatitis, and eczema from repeated exposure. An animal study indicates that MDI may induce respiratory hypersensitivity upon dermal exposure. Prolonged contact can cause reddening, swelling, rash, scaling, or blistering.

Effects on Ingestion

The effects of ingestion include irritation of the mouth, esophagus, and stomach. The harm that occurs will be a result of this irritation and not any system toxicity. The LD50 (oral- rat) for MDI is greater than 2,000 mg/kg.

Chronic Hazards

Repeated overexposure of the skin, the eyes, nose, or upper respiratory tract may cause chronic irritation. Some individuals may develop a hypersensitivity to MDI vapors and, upon exposure to minute amounts of this material, experience difficulty in breathing. Long-term overexposure to diisocyanates has also been reported to cause lung damage, including reduced lung function, which may be permanent.

Sensitization

Sensitization is an effect whereby a physiological response (e.g., respiratory or dermal) is caused by re-exposure to a low concentration of chemical in an individual following higher, initial acute exposure, or chronic exposures. The response may be immediate, delayed, or both.

The symptoms associated with respiratory sensitization by diisocyanates are similar to those of asthma. These include difficulty in breathing, chest tightness, wheezing, and coughing. If sensitized individuals continue to work with MDI, the latency period between exposure and the onset of symptoms may be shortened, and the severity of the symptoms may increase. Upon removal from MDI exposure, the sensitized individuals’ respiratory problems usually improve. If a sensitized person continues to be exposed, his/her respiratory problems can become permanent. Therefore, early recognition of sensitization by a physician specialized in lung diseases and prevention of subsequent exposure is important to protect the respiratory health of sensitized workers. It is believed that cross-
sensitization may occur between different isocyanates. Meaning individuals sensitized to other isocyanates may also demonstrate sensitization to MDI. Responses in sensitized individuals vary considerably from one individual to another.

The determination of what constitutes a significant MDI exposure can be difficult. The minimum concentration of MDI in the atmosphere that will cause subjective symptoms and objective physical findings in any given individual is unknown, especially in sensitized individuals. If anyone experiences an exposure severe enough to develop symptoms, no matter how mild those symptoms may appear, a physician should be consulted prior to resumption of work with MDI.

First Aid

First Aid in Case of Inhalation

Affected persons should exit the contaminated area to fresh air supply immediately. Remove all contaminated clothing and contact medical personnel immediately.

Keep affected persons comfortable and warm. Medication will rarely be necessary if adequate fresh air is immediately available.

If there has been a severe exposure and breathing stops, artificial respiration should be initiated immediately. If oxygen inhalation equipment is available, oxygen should be administered by a physician or authorized person.

Never attempt to give anything by mouth to an unconscious person. Medication should be given only under the direction of an attending physician. In the event of breathing difficulty, a physician or authorized person should treat with medication2 to help prevent over-reaction of the immune system and pulmonary edema.

In cases of exposure to mists or liquid MDI, immediate decontamination is essential. First responders must wear respiratory protection and avoid direct skin contact with contaminated surfaces, skin, and clothing.

First Aid in Case of Eye Contact

In the event MDI contacts the eyes, immediately flush affected area with running water for at least fifteen minutes. The eyelids should be held apart during washing to ensure contact of water or propylene glycol for skin cleaning with all affected tissues of the eyes. The affected person should receive medical attention, preferably from an eye
specialist, as soon as possible.

First Aid in Case of Skin Contact

Immediately move the affected person to a safety shower or other source of large amounts of water. Remove all contaminated clothing while under the shower and thoroughly wash affected areas with soap and water for at least fifteen minutes. Medical treatment should be given if skin irritation persists (e.g., redness, swelling, or burning sensation). Launder contaminated clothing in decontaminating solution and launder before reusing or destroy in cases of severe contamination. In all cases, always take precaution against additional exposure from contaminated surfaces and materials when completing these activities.

First Aid in Case of Ingestion

If MDI is ingested, immediately contact the Human Poison Control Center (1-800-222-1222). The affected person should immediately drink large amounts of water to reduce the concentration of the chemical. Vomiting should not be induced. Keep the individual calm and protect against loss of body heat. The person should be transported to a medical facility as quickly as possible. If vomiting should occur, more water should be given immediately. Never administer anything by mouth if the person is unconscious or having convulsions. Immediate medical attention should be provided.

Medical Considerations

Preplacement medical surveillance including pulmonary function testing should be given to individuals being assigned to work with MDI. All personnel should receive a thorough health appraisal, including examination of the upper respiratory tract and lungs.

Individuals with the following conditions should receive special consideration by a physician prior to placement in positions where diisocyanates may be contacted:

• Chronic diseases of the nose, throat, or lungs. 
• History or presence of asthma or asthmatic bronchitis. 
• Recurrent eczema or pulmonary sensitization.

The incidence of illness due to working with MDI will be minimized if appropriate industrial hygiene measures are consistently enforced. The duration of sensitization is not known. General practice is to consider sensitization permanent. Therefore, any sensitized individual affected by exposure to minuscule amounts of MDI should be assigned to work in an isocyanate-free environment.

Industrial Hygiene

The potential hazards associated with MDI can be avoided if workers are adequately instructed and supervised
on the proper procedures of handling MDI.

Every worker should be trained to realize that exposure to a potentially hazardous chemical requires immediate washing of affected areas using large amounts of soap and water, and that immediate attention may markedly decrease the severity of any health effects (see First Aid). Never wash affected areas with solvents, as this could increase the absorption of MDI through the skin.

Protective clothing, gloves, boots, and eye protection must be worn whenever there is any possibility of MDI exposure. Protective clothing shall be made of impervious materials. Soiled or contaminated clothing should be laundered or destroyed. Additional information is available at: https://polyurethane.americanchemistry.com/Products-Resources-and-Document-Library/ Proper respiratory protective equipment should be readily available and in good working order. Exhaust and ventilating equipment should be inspected and tested regularly to assure MDI vapors/aerosols are being controlled to acceptable levels.

Properly designed emergency showers and eyewash fountains should be placed in convenient locations wherever MDI is used. All employees should know the location and operation of this equipment. All equipment must be frequently inspected to make sure they are in proper working condition.