An alert was triggered after ten marine flares were brought to a police station.
The flares were found on a rubbish tip and taken to Lewes police station in a white van.
The driver left them in the van when he went inside to tell police about his find.
Police were worried the flares might be volatile so, as a precaution, they sealed off the area and called in the bomb disposal squad.
Drivers and pedestrians faced disruption and delays while police waited for the squad to arrive during the incident on Friday.
The flares were eventually defused and taken away.
A police spokesman said: "There was no major security incident. Officers were uncertain about how to handle the flares and so the bomb disposal squad was brought in to make sure everything was safe.
"There was some disruption to traffic while we waited for the team to arrive."
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