Description of Incident:
An operator was checking the level in a 500 gallon methanol storage tank:
- Tank was polyethylene plastic, double wall
- A worker climbed on top of the tank.
- Flammable vapour was ignited, when the worker touched the cap on the inner tank, resulting in an explosion and flash fire.
- The worker received first aid for a second degree burn to the arm.
What Caused It:
- The worker accumulated an electrostatic charge, when positioned on top of the tank
- Flammable methanol/air mixture developed inside the inner tank or interstitial space
- It was 18 degrees Celsius at the time of the incident and methanol has a flash point of 11 degrees Celsius
- Level inside the tank was low (less than 10 percent of total volume)
- Plastic is nonconductive and difficult to ground, and not recommended to store flammable liquids (as per API RP 2003)
Corrective/Preventive Actions:
- Update procedures for tank inspections, maintenance, and filling
- Under no circumstances is climbing on top of a tank permitted
- Install sight glass and piping to allow for filling from the ground level, with stinger extending to the bottom of the tank to prevent splash filling
- If it is necessary to open the tank cap, a personal ground strap must be worn in combination with gauntlet style gloves. Platforms to be provided if necessary.
Long Term Action Plan:
- Evaluate the suitability of plastic tanks for storage of flammable fluids such as methanol
CLICK HERE to see this ENFORM Alert in PDF
SAFTENG Comments: Although Methanol (as well as other alcohols) are considered CONDUCTIVE Flammable Liquids, this does NOT mean that plastic is “ok to use”. ALL flammable liquids will generate static charges and when they have proper grounding and bonding these charges can go to ground as quick as they are generated, thus keeping their level of charge below MIE’s of the material(s). HOWEVER when the charge must pass through a layer (and in this case TWO layers) of plastic to reach “ground” it really matters not that it is a CONDUCTIVE flammable liquid!!!!