Background and Overview of Hazards

Tetramethylammonium Hydroxide (TMAH) is widely used in micro- or nanofabrication as an etchant and developer, often used as an ingredient in a mixture or as a pure chemical. It is most commonly available in solution form (25%-50%) or as a pentahydrate in solid form.

TMAH is a very strong base with a pH >13 capable of corroding certain metals. Skin exposures to concentrations between 10% and 25% TMAH will cause 2nd and 3rd degree burns. It is acutely toxic upon dermal contact, ingestion, or inhalation. Exposure to >1% TMAH solutions over a few percent of the body must be treated as a life-threatening event.

Exposure may result in intense burning of the eyes, nose, throat, lungs and skin. Depending on the level and duration of exposure, signs and symptoms may include blurred or double vision; pinpoint pupils; changes in heart rate and blood pressure; abdominal cramping, nausea and vomiting; diarrhea, excessive salivation sweating or bronchial secretions; urinary incontinence; muscle twitching, tremors or convulsions. Since 2007, there have been several recorded fatalities from skin exposure to TMAH solutions. In addition to the alkalinity-related chemical burn, dermal exposure to TMAH may also result in respiratory failure and/or sudden death. There is no known antidote for TMAH poisoning. Understanding risks and appropriate response, adherence to standard operation procedures, and the use of appropriate protective personal equipment are all important in the prevention of occupational exposures to TMAH and related toxicity.

TMAH is identified by the following GHS warning symbols.

Responsibilities

Before using this chemical, supervisors and researchers must ensure the following.

• Understand the hazards related to TMAH and the need for safety precautions.
• Receive adequate training to use this chemical and demonstrate proficiency under supervision.
• Review the Safety Data Sheet (SDS) for hazard information.
• Establish a clear Standard Operating Procedure (SOP) along with risk assessments to understand the risks involved and how to minimize them.
• Maintain training records.
• Know how to respond to emergency situations and first aid measures.
• Work with TMAH only under the buddy system and never when alone.
• Know the location of the safety shower/eye wash and spill kit.

Eliminating/Reducing the Hazard

Determine if your application can use a TMAH alternative that is less hazardous and has a higher LD50 value to reduce the risks involved.

Order only the lowest amounts and most dilute solutions available that will meet your experimental needs.

Safe Handling

Depending on the concentrations and procedures used, handling TMAH requires personal protective equipment beyond the minimum used when handling corrosives.

Eye/face protection: A full face-shield (8-inch minimum) over a tightly fitting NISOH approved safety goggles must be worn when handling TMAH.

Skin protection: Always handle the chemical with appropriate gloves with long cuffs. Use proper glove removal technique (without touching the glove's outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use as chemical waste. Wash and dry hands after use. Glove-manufacturer’s compatibility charts do not often include data specifically for TMAH. Check the Safety Data Sheet and manufacturer’s website to determine the best gloves for your application. For full contact, Sigma Aldrich recommends Material: Nitrile rubber Minimum layer thickness: 0.11 mm Break through time: 480 min Material tested:Dermatril® (Aldrich Z677272).

Inhalation: Perform all operations in a certified chemical fume hood with the sash lowered. Always work at least 6 inches into the fume hood and behind the sash.

Clothing: A chemical resistant apron or smock over a lab coat with long sleeves should be worn when handling TMAH solutions. No exposed skin is allowed; long pants, sleeves, and closed toe shoes / boots must be worn.

Emergency Procedures

Early decontamination by irrigation with copious water appears to be the most important procedure to prevent TMAH-related systemic toxicity given that TMAH is highly soluble in water. Seeking medical attention immediately after exposure is critical.

Skin Contact In case of skin contact: Take off immediately all contaminated clothing. Rinse skin with water/ shower. Call a physician immediately.

Eye Contact After eye contact: rinse out with plenty of water. Call an ophthalmologist immediately. Remove contact lenses

Inhalation After inhalation: fresh air. If breathing is difficult, administer oxygen. Call a physician immediately.

Provide the medical team with the Safety Data Sheet SDS for the base.

Spills

General procedures for chemicals spill response apply here as well. Soak up with inert absorbent material and dispose of as hazardous waste. Keep in suitable, closed containers for disposal. Avoid generation of dusts in the case of TMAH powder.

Storage

TMAH solutions should be kept tightly closed in a dry and well-ventilated place. TMAH in solid form should be stored under inert gas since it is air sensitive and hygroscopic. Keep locked up or in an area accessible only to qualified or authorized persons.

Store away from incompatible materials like Aluminum, Alkali metals, Strong oxidizing agents, Acids, Acid chlorides, Acid anhydrides, Halogens

Waste Disposal

Do not combine waste streams containing TMAH with other chemical waste.  Collect all TMAH separately, and store and label it according to the hazardous waste management guidelines. Dispose of through the DRS chemical waste program.

References

Wu CL, Su SB, Chen JL, Lin HJ, Guo HR. Mortality from dermal exposure to tetramethylammonium hydroxide. J Occup Health 2008; 50:99–102.

Ho CK. Two fatal case reports of tetramethylammonium hydroxide intoxication: new challenge for the widely used but life-threatening substance; 2007 International Conference for Chemical Disasters and Medical Preparedness in Taiwan, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan, 22–23 June 2007.

*https://www.sigmaaldrich.com/US/en/sds/sigma/t7505 (Revision 6.5, 06/01/2021)

*https://www.sigmaaldrich.com/US/en/sds/sial/331635 (Revisions 6.5, 03/26/2021)

https://pubchem.ncbi.nlm.nih.gov/compound/Tetramethylammonium-hydroxide#section=Decomposition