A data processing apparatus and method are provided for performing hazard detection in a series of access requests issued by processing circuitry for handling by one or more slaves. The requests include one or more write access requests to be performec by an addressed slave device. Hazard detection circuitry comprises a pending write access history storage having at least one buffer and at least one counter for keeping a record of each pending write access request. Update circuitry responds receipt of a write access request to perform an update process to identify that write access request as a pending write access request in one of the buffers, and if the identity of another pending write access request is overwritten by that update process, to increment a count value a counter. Hazard checking circuitry is then responsive to at least a subset of the access requests to be issued by the processing circuitry, to reference pending write access history storage in order to determine whether a hazard condition occurs. The manner in which the update circuitry jses a combination of buffers aid counters to keep a record of each pending write access request provides improved performance with respect to known prior art techniques, without the hardware cost that would be associated with increasing the number of buffers.