Release and ignition when starting operation of a new hydrogen line

The operators involved had begun work to purge a new hydrogen 6" line into service. The required pre-work had been completed, and one operator was at the valve station preparing to slowly let hydrogen into the line, from an adjacent 8" line, which was already in service.
The second operator was at the valve station vent, to monitor purge gas flow and purity. The second operator mistakenly thought that the purge had already started, and thought that there was insufficient purge flow at the vent. He decided to open the isolation valve to the pressurized 8" line at his end. By opening the valve, he caused a high-volume flow of hydrogen through the adjacent vent pipe, which ignited.
The second operator received burns to his hands and face. A company truck was destroyed and other vehicles were damaged.

[Note of HIAD event validator: the PHMSA text is unclear on a point which hinders the understanding of the accidental sequence: the report mention that pre-works were completed, suggesting that the real works had still to start. However, immediately aftre the completion of pre-work, workers started already to inject hydrogen through a new pipeline up to the vent. PHMSA reprot calls this a purge, but it is not clear how the section of pipeline had been beofe purged with an inert gas. ].

INITIATING CAUSE is the erroneous injection of hydrogen high flow into the vent pipe
The ROOT CAUSE relates to the wrong execution of a procedure, and probably also to lack of clarity of it. Moreover, failing in recognising the hazards related to actions performed by two workers who were depending on mutual understanding, caused the lack of automatic measures preventing misunderstanding and perceptive assumptions.

pipeline, vent

The operation which brought to the incident consisted in preparing a new pipeline for its first operation.

An employee received burns to hands and face.
A company truck was destroyed and other vehicles were damaged.

none

In this accident, two employees at different location were supposed to execute a series of operations depending of each-others. It went wrong because of the assumption of one of the two, on the actions taken by the other.
The incident has been attributed to a failure to follow the procedure. However, this error could have been minimise by:
(1) Ensuring the availability of proper communication means.
(2) Introduce automatic safeguards, so that the one employee could not process at a next step without cling the previous step.