Rebecca Thomas, 24, of Johnston and Darren Griffiths, 37, of Pembroke Dock, appeared from custody at Haverfordwest magistrates court on Wednesday, August 21.
They face a joint charge of arson with intent to endanger life.
It is alleged that the pair set fire to a mattress which damaged a block of flats belonging to Pembrokeshire County Council on the Mount Estate, Milford Haven in the early hours of Monday morning, August 19.
No pleas were entered and both will next appear at Swansea crown court on September 20.
They were remanded into custody until their next hearing.
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