FDA has received an increasing number of reports of explosions involving solutions containing sodium azide used in clinical facilities. This communication is to remind laboratories and hospitals about the danger posed by long-term accumulation of sodium azide solutions, and to recommend steps to prevent such incidents.
Background – Nature of the Risks
Sodium azide is known to be explosive when heated near its decomposition temperature (300 degrees Celsius) or when it comes in contact with certain metals. Low concentrations of sodium azide are used in many clinical laboratory instrument reagents, including those for chemistry, coagulation, hematology and immunology analyzers. It is also used as a chemical preservative of samples and stock solutions in hospitals and laboratories. Sodium azide is safe to use in these reagents because it is diluted. However, failure to follow proper flushing procedures when disposing of sodium azide solutions down drain lines increases the likelihood of an explosive reaction with metal pipes.
Explosions can occur in metal drain pipes or surfaces (such as lead, copper, brass or solder) and on laboratory instruments, where the chemical may be concentrated due to such events as leakage, spills, and splashes. It can also occur as a result of improper waste disposal or improper storage of instrument parts exposed to the chemical.
Laboratory staff should be aware of the following safety considerations when using sodium azide solutions:
- A hazardous situation can arise over time when solutions of dilute sodium azide are not properly flushed down metal drains.
- The accumulation of dried, concentrated sodium azide in drain pipes and on metal surfaces increases the chance of explosions and other serious incidents.
- The danger of explosion occurs when this highly toxic chemical accumulates and is subsequently exposed to friction, heat, or shock.
Examples of Events Reported to FDA
In one incident, waste accumulated in sinks with copper pipes because of insufficient flushing. Subsequent efforts to perform maintenance where the sodium azide had accumulated resulted in an explosion when the dried chemical was disturbed. In another instance, an explosion occurred when workers attempted to remove corrosion from copper ground wires on an instrument that was located near an area used for reagent waste disposal. Another report described an explosion when old instrument analyzer tubing was disturbed. Reported injuries include cuts requiring stitches, debris in the eyes, and psychological trauma.
How can Laboratorians Protect Themselves?
All laboratory personnel should be properly trained on safe handling and storage of sodium azide. Laboratorians can eliminate or minimize the risk of harm from sodium azide solutions by following these precautions:
- Always use proper personal protective equipment, such as gloves and eye protection.
- Avoid sodium azide contact with acids or heavy metals where there is potential for sodium azide to become concentrated.
- Avoid touching or replacing corroded materials if the corrosion may be due to sodium azide; contact the manufacturer for guidance on how to clean or replace corroded parts.
- Avoid exposure of potentially concentrated sodium azide to friction or shock.
- Do not store tubing or other materials that may have been in contact with solutions containing sodium azide.
- Collect sodium azide waste into a plastic reservoir and label the container with the proper name.
- Clearly label all medical devices, collection containers and waste disposal fixtures that use products containing sodium azide.
- Follow local, State and Federal regulations regarding handling and disposal of hazardous waste, including potentially explosive materials such as accumulated or concentrated sodium azide.
- Dispose of solutions per instrument and analyzer label instructions.
- Contain waste in plastic receptacles intended for hazardous material as per Material Safety Data Sheet (MSDS) guidelines.
- If no other disposal mechanisms are available, the Clean Water Act allows disposal in sanitary sewer systems if the concentration is less than 1% of total annual waste water from facility.
- If you dispose of waste using the sewer system, flush sodium azide solutions with at least 100-fold excess of water.
- FDA Safety Alert: Sodium Azide Contamination of Hemodialysis Water Supplies
- CDC: Facts About Sodium Azide
- Northeastern University: Sodium Azide
- The National Academies Press: Disposal of Waste
For questions regarding this communication contact:
Ms. Jean Cooper
Food and Drug Administration
Center for Devices and Radiological Health
Office of In Vitro Diagnostic Device Evaluation and Safety
10903 New Hampshire Avenue
Silver Spring, MD 20993
Phone: (301) 796-6141