It’s no question that when you’re talking chemicals in any industry, questions relating to safety begin to overwhelm the conversation. For instance, a conversation surrounding food processing can ultimately lead to an attempt to understand how chlorine is used safely in the facility. One may also wonder how exposure to hydrazine when testing rocket fuels is measured. And even the safety of manufacturing chemicals in plastics production. These questions oftentimes lead to a similar response by industry professionals. No matter how it is done, reliable safety systems and chemical detection are key to ensuring a safe environment. No matter the situation, it is universally understood that safety comes first. But what happens when we differ on the severity of a chemical situation? This is often a question asked surrounding the chemical aspect of polyurethane safety.

A little about the industry

Methylenediphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) are two of the chemicals used throughout this industry and are likely some of the most important while also posing significant risk to their users.  If you are a part of the polyurethanes industry, you’ve likely hear the debate about which is safer. In the realm of industrial chemicals, MDI and TDI are two compounds that deserve close scrutiny due to their widespread use and associated health risks. These diisocyanates have distinct characteristics, applications, and potential dangers, making it crucial to comprehend their differences to ensure safe handling and mitigate occupational and environmental risks.

One of the biggest misconceptions concerning these two chemicals is that one is much more dangerous than the other. That however is not the case; both pose a great potential for harm to anyone working with them. They each have unique risk factors based on their physical characteristics and how they are used. The main risk factors can be seen in the following areas: Their physical traits, how they are used, and their unique risks.

Let’s discuss the two and their specific risk factors…

MDI is a solid at room temperature allowing for a lower risk factor for aerosolization in that form. This generally leads people to suggest that MDI is the ‘safer’ chemical in polyurethane manufacturing. In actuality, its risks primarily stem from its potential for skin and respiratory exposure during the handling of its powdered or liquid forms. Unlike the common suggestion, the primary risk factor with MDI is its ability to generate aerosols, which can lead to inhalation exposure. Respiratory exposure to MDI is a significant concern, as it can lead to symptoms such as coughing, shortness of breath, and asthma-like reactions. Long-term exposure to high concentrations of MDI is associated with the development of occupational asthma. Additionally, MDI can cause skin irritation and allergic reactions upon contact.

On the other hand, TDI presents as a liquid at room temperature and carries its own risk factors.  The primary concern with TDI is its propensity to cause skin and eye irritation upon contact due to its liquid form. It can also lead to respiratory issues if its vapors are inhaled. TDI is volatile and can readily form vapor that can be inhaled, potentially leading to symptoms like coughing, chest tightness, and wheezing. Chronic exposure to TDI is known to cause respiratory sensitization, which can result in occupational asthma.

The Process for the Product – How are TDM and MDI used?

A non-technical glance takes you into the process of foam production and polyurethane safety. There are many different ways to produce those foamy results but the two below are common practices for the industry.

The One-Shot: Think of this common practice as making soup. Everything goes into the same pot and ends up as a tasty medley of mixed vegetables, meat, spices, and broth. And the flavor can change based on what’s put in and the specific amounts of each.  When it comes to foam production, TDI or MDI is combined with additives, polyols, and catalysts which at specified amounts create the desired end result. These results can vary and can produce an end product with less consistent characteristics.

The Prepolymer: Prepolymer systems are used for a bit more control on the end product. Although we love our soup analogy used to describe the One-Shot method, prepolymers use another analogy. This method, like mixing your wet and dry ingredients separately when baking a cake, involves creating a polymer out of the TDI or MDI and polyols first. That polymer is then stored ‘unreacted’ and used at a later time in the foaming process. This allows for a bit more control (like the consistency of a well distributed batter producing a more uniform cake) and allows for more precision on some of the foams end-properties.

Each of these systems is designed to give a specific result and to utilize certain characteristics of each chemical. Both the one-shot and prepolymer systems can be adapted to open or closed systems. This depends on the specific requirements, safety considerations, and the scale of the foam production operation. Implementing closed systems is crucial in environments in order to minimize exposure to isocyanates and ensuring worker safety are top priorities.

Keeping the safety in the systems

In a closed system, the chemicals, reactions, and foam formation take place within a controlled and enclosed environment. This system minimizes exposure to isocyanates (such as TDI or MDI) and other potentially hazardous chemicals. Closed systems are preferred in industrial settings where safety and environmental concerns are paramount. They require specialized equipment and facilities to ensure that fumes, emissions, and potential leaks are effectively contained and managed.

In an open system, some of the processes may occur in a less controlled or open environment. This setup may result in a higher risk of exposure to hazardous chemicals, particularly during the mixing, pouring, or processing stages. Open systems are typically used in smaller-scale or less industrial settings. The same level of containment and control measures may not be feasible or necessary in those situations.

The less frequently considered danger of any polyurethane production method follows the production process. If the components for the mixtures used were not made at exact amounts, there could be “left-over” or unreacted TDI or MDI in the environment after production has taken place. This is a risk factor for polyurethane safety that many do not consider and can be a very dangerous situation.

Be Safe.

Safety measures in the polyurethanes industry are so prominent that rarely a conversation can exclude them. Fortunately there are many measures that facilities can implement to minimize exposure. These include: Proper ventilation, PPE, Proper training and education, and having a well-established and robust Emergency Response Plan. We personally love the addition of the SafeAir TDI/MDI badge as an employee screening or leak-detection badge. They provide an addition to already established safety plans for an added layer of safety and security.

In summary, while both MDI and TDI present health risks, the key difference in their risk factors lies in their physical states and the associated exposure routes. MDI poses a greater risk of respiratory exposure due to its potential to generate aerosols. TDI’s liquid form makes skin and eye irritation more likely upon direct contact. Awareness of these distinct risk factors is vital in formulating safety measures tailored to the specific characteristics of each diisocyanate.

Don’t forget to take a look at the other blogs in our polyurethane Series.