Chemical Data Notebook Series #17: Toluene Diisocyanate
FEATURES
HAZARDOUS MATERIALS
Toluene diisocyanate, or TDI, is a relatively stable chemical whose vapors are reported to be somewhat difficult to ignite. But, because they’re organic, ignite they can. As with any vapors that burn, any accumulation of them resulting in a mixture with air within the flammable range will produce an explosion. And exposure to TDI, its vapors, or its combustion products poses a serious health problem. The effects of inhaling TDI may be delayed and can be fatal.
TDI’s major use is in the production of thermosetting polyurethane foams and polyurethane varnishes, paints, and coatings, as well as some urethane plastics. It’s a toxic liquid, colorless to pale yellow, with a pungent, fruity odor. Its reaction to water is nonviolent, producing carbon dioxide gas and insoluble by-products, mostly polyureas. TDI will slowly polymerize (again, nonviolently) when heated to temperatures above 113° F. Its combustion products may contain cyanides and various nitrogen oxides.
The chemical formula for TDI is 2.4-CH3C6H3(NCO)2. TDI’S flash point is 270° F, its flammable range is from 0.9% to 9.5%, and its ignition temperature is 1,148° F. Its specific gravity is 1.22, vapor density is 6.0, and molecular weight is 174. It boils at 482° F and freezes at 68° F.
Health hazard
TDI’s odor may be detected at levels as low as 0.05 parts per million, with levels of 0.5 ppm causing serious health hazards. The level at which it’s immediately dangerous to life and health (its IDLH) is 10 ppm, its short-term exposure limit (STEL) is 0.02 ppm, and its threshold-limit value/timeweighted average (TLV/TWA) is 0.005 ppm.
TDI’s major hazard is its toxicity. Contact of the liquid with the skin can cause redness and blistering, as well as possible sensitization. Contact with the eyes can cause damage ranging from severe irritation to blindness. The vapors of TDI can have the same impact.
Inhalation of the vapors can cause severe bronchial irritation and may even produce symptoms resembling a heart attack. These include breathing difficulties, abdominal pains, and heavy pressure on the chest. Severe chemical pneumonitis, which can lead to severe pulmonary edema and death, is also possible. Subsequent exposures can lead to potentially fatal asthma attacks.
TDI exposure can sensitize the lungs to the vapors of other materials, particularly organic solvents. Vapors of these materials can then produce symptoms resembling those of TDI exposure, only less severe. Sensitized persons will also react to TDI released in the depolymerization of urethanes, in addition to a sensitivity to any molecule containing cyanide within its structure. Other reported systemic disorders include liver, kidney, blood, and gastrointestinal effects.
Fire hazard
As pointed out earlier, TDI’s vapors do burn and can produce an explosion, although igniting the vapors is difficult. With their tremendously high vapor density, TDI’s vapors will “hang together” and flow along low spots in the ground for great distances. The chemical’s relatively low vapor pressure indicates it’s not very volatile; nevertheless, it will produce large quantities of vapors when heated. If containers are exposed to radiated heat from any source, violent rupture is a possibility.
Any leak from the container will produce tremendous quantities of heavy, toxic, combustible vapors that will threaten all populated areas downwind. The vapors pose a serious health problem to exposed populations, and combustion products, although lighter, may be just as toxic. In any event, whether vapors or liquid are leaking, and whether burning or not, the toxic danger to populated areas must be a major concern. Evacuation procedures should be considered throughout the incident.
If the liquid has spilled and is involved in a fire, follow all rules pertaining to a combustible liquid fire. Stay upwind and avoid contact with the smoke and combustion products. If flame is impinging on the containers, they should be cooled from a safe distance with water.
Beware of the possibility of catastrophic failure of the containers. An explosion can result from pressure buildup within the container caused by evaporation of the hot liquid and inadequate (or nonexistent) venting of the vapors. The container failure is a pressure-relief explosion, followed by the explosive ignition of the released vapors.
The explosion of a container of TDI (or any other flammable or combustible liquid) will be deadly to anyone in the danger zone, which may have anywhere from a 500-foot to a 2,000-foot radius, depending on the size of the container.
Because of the toxicity and potential for ignition, it’s essential to contain TDI spills and leaks quickly and to prevent accumulation of the vapors.
In the case of leaking drums, overpacking in salvage drums will be sufficient as long as contact with the liquid or vapor is avoided.
For larger spills, containment dikes may be built using soil, sand, clay, or other absorbent materials. Trenches may be dug to lead spilled liquid into the containment area. Containment pits may also be dug as long as you don’t provide an ignition source for vapors. Although the vapors may be difficult to ignite, it’s always a good practice to work upwind of the material. If vapors are moving in an erratic pattern, water spray may be used to disperse them, taking care to contain the runoff water.
Whatever can be done to prevent the generation and movement of vapors is desirable. A deep containment pit will have a smaller surface area than a containment pond, and therefore ma^ terial contained in a pit will generate fewer vapors. A tarp or plastic cover may also be used to cover the smaller surface of the pit. However, a deep containment pit will increase the difficulty of removing contaminated soil. Also, the threat of ground water contamination increases when a pit is dug.
Whenever possible, the containment pond, trench, or ditch should be lined with film or sheets of an impervious material, such as Butyl rubber, natural rubber, or polyethylene. This lining will prevent percolation of the product into the soil. If a lining isn’t used, tests will have to be performed on the soil (after the incident has been handled) to determine how much of it will have to be dug up and removed to a secure disposal area.
In either a pit or pond, foam may be applied to the surface to slow the release of vapors. Because the foam will break down and more may need to be added, the total liquid volume must be watched to prevent runoff. The product will probably not be salvageable after repeated applications of foam are used, since the water portion of the foam will react with the TDI. As this reaction takes place, less hazardous products, such as carbon dioxide, will be formed.
Synonyms
ANTRF
benzene-2,4-diisocyanato-1 -methyl-
diisocyanatomethylbenzene
diisocyanatotoluene
diisocyanotoluene
Hylene T
isocyanic acid, methyl-mphenylene ester
isocyanic acid, methylphenylene ester
methylphenylene isocyanate
Mondur TDS
Nacconate 100
NCIc50533
Niax TDI
Niax TDI-P
TCPA
TDI
TLC
TM
TM-65
toluene diisocyanate
toluene-2.2-diisocyanate
tolydene isocyanate
tolylene diisocyanate
2.4-toluene diisocyanate
Resource Conservation and Recovery Waste Act Number U223
Identification Numbers and Ratings
United Nations/North America
UN NA 2078
STCC
(Standard Transportation Commodity Code)
4921575
CAS
(Chemical Abstract Service)
584-84-9
RTECS
(Registry of Toxic Effects of Chemical Substances)
CZ 6300000
IMO
(International Maritime Organization)
6.1, poisonous substance
National Fire Protection Association 704 rating
3-1-1
If the product does reach a waterway, all downstream users must be notified immediately. Even though the product will be reacting with the water as it moves downstream, the reaction may be slow enough that the contaminated water can produce explosions, fires, and toxic atmospheres if it’s drawn into industrial operations where it’s heated (as in a cooling operation or a boiler). If the waterway can be diked, dammed, and diverted, the water can be held in one place until all the product has reacted and converted to less hazardous materials. Then it can be released after being declared safe by the proper environmental authorities.
TDI’s specific gravity of 1.22 means that it will sink in water. Since the reaction with water is very slow, it’s possible to have significant amounts of the material flowing along the bottom of a stream or collecting in low spots of a pond or lake. In this case, the material may be pumped from underwater into secure containers. If pumping isn’t possible, dredging may remove the product and contaminated sediment. The dredged material should also be deposited in secure containers.
Clean-up
Once the TDI is contained, removal should begin immediately. The shipper or seller of the product should provide equipment to pump the product from the containment areas into secure containers. Emergency responders should refrain from clean-up operations wherever possible, leaving that task to the experts. Equipment compatible with the material must be used in all salvage operations. Care must be taken during the pumping procedures, because the TDI might solidify and plug up the pumping equipment.
As much of the TDI as possible should be removed by pumping before other techniques, such as absorption, are attempted. TDI may be absorbed by using soil, sand, clay, cement powder, sawdust, or any other absorbent material. Once the liquid has been absorbed onto the solid material, the absorbent will have all the hazards of the spilled liquid itself. It will have to be deposited in secure containers and disposed of properly.
Neutralization of the product is another technique for mitigation. If time and space are available, the TDI can be removed in small quantities and added to water in a secure area or container to produce the reaction that converts TDI to less hazardous products. At least one reference suggests the use of isopropyl alcohol (rubbing alcohol or isopropanol) and ammonia, both hazardous materials in their own right, to speed the reaction with water, but exposure of these materials and the TDI to the atmosphere during this procedure should be minimized.
Glossary
Absorption—The penetration of one substance into the inner structure of another.
Percolation—The passage of a liquid into or through a porous material.
Polymerization—A special chemical reaction whereby a material will react with itself to form an extremely long chain called a polymer.
Sensitization—A reaction in which exposure to a particular chemical will cause reactions to future exposures to be much more severe, or will cause adverse reactions to chemicals that previously caused no problem for the now-sensitized individual.
Thermoset—A class of plastics that can be subjected to heat and pressure only once. Any further exposure to heat or pressure will cause the material to decompose. Contrast with thermoplastics, which can be subjected to heat and pressure more than once.
Vapor density—The relative density of a chemical’s vapors as compared with those of clean, dry air.
Vapor pressure—The pressure exerted on the sides of a closed container by the vapors of a material at equilibrium.
In any event, if absorption or neutralization techniques are to be attempted, the aid of competent resource personnel should be enlisted. Any time firefighting personnel get involved in deliberately initiating chemical reactions at the scene of a spill, they’re opening themselves to criticism and controversy. Conversations with Chemtrec (the Chemical Manufacturers Association’s Chemical Transportation Emergency Center) should be carefully documented, as well as any conversations with chemists and other expert personnel provided by the shipper, the seller, the buyer, or any other company offering to help.
Once convinced that the situation is stabilized and there’s no immediate threat to the population, the incident commander must begin to consult environmental agencies and other experts on how to proceed. It’s not the fire department’s responsibility to clean up a chemical spill if threats to human life are removed.
First aid and protective clothing
Standard procedures are in order for anyone who has inhaled TDI vapors. That is, the victim should be moved to fresh air or have artificial respiration administered if breathing becomes difficult or stops. To prevent exposure to vapors, emergency responders who may be administering mouthto-mouth resuscitation must have protection in the form of a mask or one-way valve device. Immediate medical treatment is mandatory; so is continuing medical treatment—the victim should see a doctor again after a month or so to check whether the exposure has created a sensitivity.
A victim who has ingested TDI must be forced to swallow large amounts of water and induced to vomit. Again, medical attention must be immediate.
If skin contact has occurred, flush the skin with large amounts of soap and water. If eye contact has occurred, flush the eyes immediately with water for 15 minutes, occasionally lifting the eyelids.
All contact with skin or eyes must be prevented. Total encapsulating suits or other protective clothing must be of material impervious or resistant to TDI. Materials recommended for such suits and clothing include Butyl rubber, chlorinated polyethylene, natural rubber, polyethylene, and polyvinyl alcohol. Boots and gloves of similar materials should be used, and face shields and goggles must be worn. Positive-pressure selfcontained breathing apparatus must be used wherever TDI vapors might be involved.
