Safety Insight: Are You Using Small Plastic Containers for Flammable Liquids Safely?
Why is it important?
Flammable liquids have traditionally been stored in metal containers. Over the last 15 years, plastic containers in a wide variety of shape, size, type, and materials, have seen widespread adoption for the storage and transport of flammable liquids. NFPA 30, Flammable and Combustible Liquids Code, generally permits use of containers made from ordinary plastics if the container volume is less than 5 gallons. Unfortunately, most plastics are highly electrically insulating, cannot be grounded and tend to become electrostatically charged. This creates a risk of electrostatic discharges which are capable of igniting flammable atmospheres. As a result, a flash fire hazard exists even when relatively small containers are used. Such fires have resulted in significant damage to equipment, facility structure, injuries, and even fatalities.
Potentially incendive brush type electrostatic discharges can occur from the surface of the plastic container, or from the surface of the insulating liquid in the container. Spark type discharges can occur from charged conducting objects (either container metal components or conducting liquids), that have become isolated (e.g. by the plastic) and are unable to dissipate their charge. There are two distinct ignition hazards that must be considered with plastic containers – internal ignitions of flammable vapors and external ignitions of flammable atmospheres surrounding the container. In the case of the latter, while the contents of the plastic container may not actually be flammable, the container may serve as an ignition source from other flammable sources in the workplace!
What should be done to handle such containers safely?
- A hazard assessment should be carried out before using any size of plastic container in a flammable atmosphere or to contain flammable liquids. The assessment needs to consider the electrostatic properties of the container and the possibility of a flammable vapor or aerosol mist being produced from the liquid, bearing in mind flashpoint and process ambient conditions.
- Measures to control flash fire hazards associated with use of small plastic containers could include (but not be limited to):
- Grounding/bonding of the container metal components (if applicable)
- Avoiding high velocity liquid splash filling
- Use of ionizers for electrostatic charge neutralization of plastic surfaces
- Use of mechanical dilution ventilation, or conducting transfers outdoors in well ventilated areas
- Secondary spill containment
- Proper PPE for operators conducting transfers – flame resistant clothing (FRC), gloves and full face shields
- Operator training