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Corrosive Liquid Spill

Background

For a manufacture, Sulphuric Acid had to be mixed with two other components.  Because of increased demand for the product the process had been transferred from the vessels normally used to 2 larger vessels.  The components had to be loaded from drum stock via the bottom valve of the stirring vessel.

The Accident

After having loaded the three components with a total weight of about 4500kg, the operator had removed the drums used in the Sulphuric Acid feed and was disconnecting the pump from the bottom valve on the vessel.  This connection was a flexible hose with Camlock fittings at each end, which had been connected to the bottom valve on the tank and the additional valve on the pump outlet.  Thinking he had closed the valve at the bottom of the vessel he disconnected the Camlock from the vessel.  He noticed the presence of some product, not immediately rushing out, but after a second or two it began to rush out from the connection at the base of the vessel.  He attempted to reconnect the Camlock fitting, but was splashed by the product discharging from the flexible fitting, on the open bottom valve, resulting in chemical burns to his upper chest, arms and legs.  After initial response to quickly close the valve, contain the spill and commence clean-up by the Site Emergency Response Team, the incident was controlled by the Police and the Fire Brigade.  The operator was taken to hospital by ambulance.  There was no loss to the environment.

Measures taken

The investigation team developed an action plan to eliminate or reduce the risk associated with this process. During this development, some actions were identified that refer to risks not directly related to this accident or are related to analogous processes and equipment.  These are not listed here.

  1. Install feed from top of vessel
  2. Label valve "OPEN/CLOSE"
  3. Extend valve handle for easier handling and better visibility of valve position
  4. Establish clear procedure and batch card for the process in the large vessels
  5. Install bleed valve on all pumps
  6. Improve personal protection equipment for this process
  7. Review possibility of hard pipe for material feed
  8. Review possibility to substitute Sulphuric Acid
  9. Outlet of vessel redirected downwards and to the side, away from any operating position

Lessons learned

Moreover

In the discussion subsequent to the accident it was concluded that the base valve of such a vessel should ideally not be a quick action butterfly type.  As a rule it would be a ball valve, a cone and seat valve fitted into the base of the vessel, or at least a threaded gate valve to provide a controlled release of the vessel contents.  The final choice needs to be based on local conditions.

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