Many chemicals used in the research laboratory when stored for prolonged periods or under improper storage conditions can become unstable or may form explosive chemical products.  Examples of these chemicals include peroxidizables and polynitrated aromatics.  Some chemicals may also present special hazards after prolonged storage.  Examples are chloroform, formic acid and anhydrous hydrofluoric acid.  There have been accidents in overseas or local universities involving time sensitive chemicals.  The root causes of these accidents are the failure to have a procedure in place to track and inspect these time sensitive chemicals and the failure to understand these hazards/decomposition products. 

Based loosely on those unsafe properties that can develop, the following are general categories of time sensitive chemicals:

1. Peroxide formers and chemicals that undergo hazardous polymerizations 
These are peroxidizables or oxygenated organic compounds that form explosive levels of peroxides after prolonged storage and exposure to air.  Polymerization of some of these creates additional hazards of unstable compounds.

2. Evaporation hazard
Stabilized or wet chemicals can become shock or friction sensitive when the stabilizer evaporates or upon desiccation.  These compounds are typically polynitrated aromatics with picric acid being the most notable. 



3. Materials that generate significant additional hazards by undergoing slow chemical reactions over time



Chloroform will react with air over time at room temperature to form phosgene which is a highly toxic gas.  The phosgene formed is both stable and soluble in chloroform.  Anhydrous hydrofluoric acid easily liquefies and can react with a carbon steel cylinder to form hydrogen and can cause an increase in pressure inside the cylinder.  Concentrated formic acid (90-100%) slowly decomposes to form carbon monoxide and water upon prolonged storage.  Gas pressure has been reported to reach 101 psig within a year of storage which can be sufficient to rupture a glass container.

Researchers should always review the MSDSs and research information on the storage and decomposition products of their time sensitive chemicals.  The MSDS will state whether it is unstable under certain conditions or after storage for a period of time, and this information should be highlighted in the risk assessment.

The following will assist you in identifying time sensitive chemicals present in your laboratory and help you safely manage the risks associated with those chemicals. 

• Identify time sensitive chemicals in your inventory; define the storage conditions and track time sensitive materials by maintaining a time log.  Check peroxide forming chemicals every 3 months using peroxide test strips which can be obtained at the warehouse of the Center of Laboratory Supplies (CLS).
  
  On campus, the chemicals ordered and delivered via the Center of Laboratory Supplies (CLS) Chemical and Dangerous Goods unit will be listed on the laboratory chemical inventory database under your room’s records.  You should make use of this central inventory system to mark all time sensitive chemicals with the date when the container is opened, and the date when the peroxide is tested/ inspected.  For time sensitive chemicals you have marked opened in the central inventory system, you will receive an e-mail alert every 3 months to ensure a timely peroxide test.
   
• Containers should be inspected periodically to verify their condition.  In general, all chemical containers should be inspected at least every 6 months.
  
  Peroxidizables may be characterized by having a "mossy" look around the cap.  There may be a white film or residue around the neck, threads or cap of the container.  Other signs of peroxide formation include crystals in the container or discoloration of liquids.  Polynitrated aromatics (e.g. picric acid) which have dehydrated will be pale in color and crystals will be formed.
  
  If you discover time sensitive chemicals that have expired or are undated, visually inspect for water content, discoloration, crystal deposits on the walls, and white residue around the neck or lid.  Do not attempt to remove the cap.  If suspected materials are recognized, do not handle the container. Mark the container and notify HSEO for assistance.

For more information and a list of peroxide forming chemicals and chemicals which present hazards after prolonged storage, please visit the following reference:
http://www.ab.ust.hk/hseo/sm06/app/app08b.htm