Christopher Saunders-Pope, from Wilton, was jailed for child sex offences and drug possession.
A councillor said local firefighters were among the responders to the Novichok poisonings in 2018.
Dorset and Wiltshire Fire and Rescue Service says it needs to close stations to save money.
Campaigners pulled the stunt in Dorchester over proposals to close eight fire stations.
A road closure is in place and police have warned people to avoid the area.
Wilton firms say they are paying six to seven times what they used to on energy.
Bosses at Huntsman could decide next week whether to close its Wilton plant in Redcar.
The fire service has proposed closing four on-call stations in Dorset and four in Wiltshire.
A consultation will open into plans to close eight fire stations across Wiltshire and Dorset.
