Published on 11/01/24 507 Views

One of two operators preparing equipment for maintenance in the sulphuric acid alkylation unit attempted to open a manually-operated quarter turn plug valve in the suction line of the standby isobutane recycle pump. However, the gearbox was found to be inoperable. One of the operators extracted the 4 vertical bolts which connected the gearbox support bracket to the valve body and removed the faulty gearbox so the valve stem could be turned using a pipe wrench. However, these same bolts also secured the pressure-retaining bonne (“top-cap”). When the valve stem was turned, the bonnet separated from the valve body, releasing ~910kg (2000 lb) of pressurised isobutane liquid to atmosphere. The escaping liquid formed a flammable vapour cloud which travelled ~20m (70ft) within 30 seconds and found an ignition source. The resulting fire severely burned an operator and 3 contractors who were working in the vicinity.

Ask yourself and your crew:

How can something like this happen here (e.g. on our site)?
What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
How do we know the risk controls/barriers are working?
What improvements or changes should we make to the procedures, controls/barriers or the way we work?

Original content courtesy of IChemE Safety Centre