Pyrophoric materials are those that are capable of spontaneous combustion in the presence of air. Spontaneous ignition or combustion takes place when these substances reach ignition temperature without application of external heat. Ignition may be delayed or only occur if the material is finely divided or spread as a diffuse layer (titanium powder is an example in the first case, and mixed tributyl phosphine isomers is an example in the second). Ignition can be instantaneous, such as with trimethylaluminum. The following classes of compounds are prone to pyrophoricity. These materials burn at high temperatures and will react violently with water, air, and/or other chemicals. Handle with care!
Classes of Pyrophoric Compounds
- Finely divided metals (calcium, zirconium)
- Alkali metals (sodium, potassium)
- Metal hydrides or nonmetal hydrides (germane, diborane, sodium hydride, lithium aluminum hydride)
- Grignard reagents (compounds of the form RMgX)
- Partially or fully alkylated derivatives of metal and nonmetal hydrides (diethylaluminum hydride, trimethylphosphine)
- Alkylated metal alkoxides or nonmetal halides (diethylethoxyaluminum, dichloro(methyl)silane)
- Metal carbonyls (pentacarbonyliron, octacarbonyldicobalt, nickel carbonyl)
- Used hydrogenation catalysts (especially hazardous because of the adsorbed hydrogen)
- Phosphorus (white)
Pyrophoric materials should be stored in tightly closed containers under an inert atmosphere or liquid. All transfers and manipulations of them must also be carried out under an inert atmosphere or liquid.
Personal Protective Equipment (PPE)
- Wear closed toed shoes made of a nonporous material, leather is preferred.
- Use a face shield and chemical splash goggles to protect your face.
- Wear a flame resistant labcoat/apron or cloth labcoat/apron that can be quickly removed if needed.
- Do not use plastic that can melt and adhere to your clothing/skin in event of a fire.
- Use gloves made of a material resistant to the solvent/reagent.
- Fire-resistant outer gloves with good dexterity are recommended.
- Know where the nearest safety shower is from the reaction area.
Required Work Practices
The following general guidelines must be followed while working with pyrophoric materials.
Know the properties and hazards of all chemicals you are using.
Select and obtain all necessary materials to dispense and use the reagent(s) safely.
- Dryboxes are used to supply an inert atmosphere to prevent pyrophoric reactions with air.
- Fumehoods do not supply an inert atmosphere; however, they can be used for ventilation and staging the reaction apparatus. The sash should be kept lowered to assist with containment in event of a violent reaction and to provide a barrier between the lab worker and the reaction.
Transferring Liquid Pyrophorics
Flex syringes (double-tipped needles) can be used for transferring materials. Flex syringes are constructed of tubing with needles attached to both ends for materials transfer through septa. A supply of low-pressure inert gas can be used to introduce the material to a reaction vessel, graduated addition funnel or graduated syringe. Tubing with a single needle may be needed to introduce the inert gas.
Appropriate glassware and reaction equipment
- Ensure your glassware is DRY before assembly and introducing pyrophorics
- Thoroughly purge all air from the apparatus with the proper inert gas
- Use secure fittings, keep air-tight with a light coat of vacuum grease
- Secure septa to all addition/withdrawal orifices
- Incorporate bubblers filled with mineral oil to prevent air backflow
- Use pressure rated glassware and fittings for pressurized reactions
Inert gas for purging air and material transfer
- Nitrogen is not suitable for all materials, consult the MSDS
Syringes may also be used to withdraw small quantities of liquid reagent (<50 mL) from containers when a supply of inert gas is provided to displace the quantity withdrawn.
- Ensure the syringe is completely DRY and purged with appropriate inert gas
- Insert a line into the septum, connected to a mineral oil-filled bubbler to prevent overpressure
- Insert a low-pressure inert gas source line into the septum
- Insert an extraction syringe into the septum and slowly withdraw reagent
Never work alone with pyrophorics. Ensure someone can see or hear you.
Purchase quantities that will ensure use of the entire product within one year.
Use containers with transfer septa (i.e. Aldrich Sure/Seal) for liquid reagents.
- Septa prevent exposure to air and moisture and allow you to safely transfer the pyrophoric material when an inert working atmosphere is not available.
Visually check the container and reaction vessel septa for degradation before use.
Emergency ProceduresA Class D fire extinguisher or powdered lime should be available in the lab.
- ABC and CO2 extinguishers can cause some pyrophorics to react more vigorously.
- Powdered lime can be used to cover spills and slow the reaction with air/humidity.
- Lime is hydroscopic; keep storage containers closed to prevent absorption of atmospheric moisture.
Do not clean up spills. Contain the spill and/or extinguish the fire only if you can do so safely. Evacuate the lab and contact EHS (512-471-3511) immediately.