Markers warning paramedics that they may face violence or aggression have been placed on nearly 50 properties in Wigan.
In the past year North West Ambulance Service (NWAS) has placed 19 violence and aggression markers on properties in the borough, according to figures released under of freedom of information laws.
Aggression markers are placed on addresses when individuals have previously demonstrated threatening behaviour or physical violence towards ambulance crews.
They warn paramedics to proceed with caution and in some cases, can mean police officers are also requested to attend as well to ensure their safety.
This is an increase from just five in 2014 - although the markers have only been recorded since August that year - and 15 in 2015.
A spokesman for NWAS said this was only ever done using a robust system and they are constantly reviewed to ensure the safety of its staff.
He said: “Our ambulance crews work extremely hard to help people and save lives and it is unfortunate that the trust has to put such measures in place to protect our crews from violence.
“The trust has a robust system for the application and review of violence and aggression address markers in the region.
“Violence and aggression flags are applied to specific addresses to ensure the safety of our staff, allowing the trust to understand where violent or aggressive patients reside.
“Flags applied to a specific address may be a result of previous experiences of our crews when responding to incidents.
“Flags applied to addresses are supported by incident reports, providing evidence as to why the flag is in place and are regularly reviewed.
“When responding to incidents at such addresses our staff will be informed if a patient has a history of violent or aggressive behaviour and will proceed with caution.
“If crews attend incidents at the addresses of patients with a history of more serious violence the crews may be escorted by the police.”
Jeff Gorman, NWAS UNISON Branch Secretary, which represents paramedics, said they often face violence when the call has been made by a passerby and not the person requiring attention.
He said: “Ambulance staff sometimes attend incidents that have been reported by a passerby.
“The person who needs help might not know that the ambulance is coming, and sometimes they respond with hostility or even violence towards ambulance staff.
“This is especially the case if the patient is under the influence of drink or drugs, or is particularly distressed.
“Ambulance staff often have to negotiate access or consent in order to assist a patient. They work in uncontrolled environments where they have to expect the unexpected.
“The robust system of flagging properties where there have been problems in the past is useful in alerting crews to where they need to exercise extra caution.”