4. Health Considerations

Acute Hazards

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

In the United States, vapor levels of TDI are to be controlled according to standards established by the Occupational Safety and Health Administration (OSHA). The current OSHA permissible exposure limit (PEL) for TDI is 0.005 ppm as an 8-hour time-weighted average (TWA) concentration and as a ceiling concentration of 0.02 ppm. Another group who has established guidelines for TDI exposure is the American Conference of Governmental Industrial Hygienists (ACGIH), a non-governmental organization (NGO). They have established a threshold limit value (TLV) for TDI at 0.001 ppm (1 ppb) as an 8-hour TWA concentration and 0.005 ppm (5 ppb) as a STEL / ceiling limit.

In Canada, occupational exposure limits are regulated within each Province. Some provinces adopt exposure limits established by the ACGIH (an NGO). Mexico also adopts the ACGIH exposure limits.

 

Effects on the Respiratory System

Exposure to TDI above allowable vapor concentrations may cause irritation to the mucous membranes of the upper and lower respiratory tracts. Even very brief exposures to TDI vapors may cause difficult or labored breathing, throat dryness, headaches, and chest discomfort. Severe overexposure may result in bronchitis and pulmonary edema. The symptoms of exposure may be delayed, and an allergic reaction can appear in susceptible persons. The health of all personnel associated with the handling of TDI should be monitored regularly.

 

Effects on Eyes

Brief exposure to TDI vapors may cause mild irritation and watering. The symptoms of direct eye contact with TDI liquid or high concentrations of vapors are severe watering, irritation, and inflammation of mucous membranes. Corneal opacity and discharge may result.

 

Effects on Skin

Skin contact with TDI may result in irritation and a mild tanning. Direct contact may produce skin sensitization, contact dermatitis, and eczema from repeated exposures. Animal studies indicate that TDI may induce respiratory hypersensitivity upon dermal exposure.

 

Effects on Ingestion

The effects of ingestion include the irritation and burning of the mouth, esophagus, and stomach. The harm that occurs will be a result of this irritation and not of any systemic toxicity. The LD50 (oral-rat) for TDI is 6,170 mg/kg.

 

Chronic Hazards

Repeated overexposure of the skin, the eyes, nose, or upper respiratory tract may cause chronic irritation. Exposure above the PEL may result in bronchitis, bronchial spasms, and pulmonary edema. Long-term exposure to TDI has been reported to cause lung damage including reduced lung function that may be permanent.

Some individuals may develop a hypersensitivity to TDI vapors and may experience a severe reaction when exposed to TDI vapors at concentrations below established guidelines. Symptoms of hypersensitivity to TDI may include wheezing, shortness of breath, and difficulty in breathing (See Sensitization).

A study by the National Toxicology Program (NTP) reported increased numbers of tumors in rats and mice dosed orally with TDI. However, several deficiencies have been cited which may compromise the validity of the study. Another chronic inhalation study indicated no increase in tumors in rats and mice when exposed to TDI at occupational levels.

In general, TDI is not anticipated to represent a significant cancer hazard when atmospheric levels are maintained below the recommended exposure guidelines.

 

Sensitization

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

The symptoms associated with respiratory sensitization by diisocyanates are those of asthma. These include difficulty in breathing, chest tightness, wheezing, and coughing are common symptoms. If sensitized individuals continue to work with TDI, the latency period between exposure and onset of symptoms may be shortened, and the severity of the symptoms may increase. Many experts believe that early diagnosis of sensitization and removal from subsequent exposure can prevent permanent lung damage. Long-term, perhaps permanent lung damage and even death can result when sensitized individuals continue to have exposures to TDI. It is believed that cross sensitization may occur between different diisocyanates. Individuals who are sensitized to other diisocyanates may also demonstrate sensitization to TDI.

The PEL values and ceiling limits should be sufficiently low to prevent sensitization in most individuals. However, allergic reactions may occur in sensitized individuals at concentrations well below these values. Once sensitized, individuals must be excluded from further exposure. The determination of what constitutes a significant TDI exposure can be difficult. The minimum concentration of TDI in the atmosphere that will cause subjective symptoms and objective physical findings in any given individual is unknown, especially in sensitized individuals. Responses in sensitized individuals vary considerably from one individual to another.

The odor threshold for TDI (0.2 – 0.4 ppm) is above the PEL value. TDI, therefore, has poor warning properties. The detection of TDI odor indicates overexposure. If anyone experiences an exposure severe enough to develop symptoms, no matter how mild, a physician should be consulted immediately.

 

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 TDI, 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 TDI comes in contact with the eyes, immediately flush affected area with running water for at least 15 minutes. The eyelids should be held apart during washing to ensure contact of water with all affected tissues of the eyes and eyelids. 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 or propylene glycol for skin cleaning for at least fifteen minutes. Medical treatment should be given if irritation including redness, swelling, or a burning sensation persists. Launder contaminated clothing before reusing and destroy in cases of severe contamination. In all cases, always take precaution against additional exposure from contaminated surfaces and materials.

First aid in case of ingestion

If TDI 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 give fluids or induce vomiting 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 TDI. All personnel should receive a thorough health appraisal, emphasizing an examination of the respiratory tract.³

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 of or presence of asthma or asthmatic bronchitis
• Recurrent eczema or pulmonary sensitization

The incidence of illness due to working with TDI will be minimized if reasonable and acceptable 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 miniscule amounts of TDI should be assigned to work in an isocyanate-free environment.

 

Industrial Hygiene

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

Every worker should be trained that exposure to a 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 area with solvents as this could increase the absorption of TDI through the skin.

Protective clothing, gloves, boots and eye protection must be worn whenever there is any possibility of TDI 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 TDI vapors/aerosols are being controlled to acceptable levels.

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