Gas safety valve comprising: - a valve body which defines an inlet, an outlet and a flow pipe connecting said inlet to said outlet; - a shutter located in said flow pipe and movable between an open position, in which said shutter allows the flow of an operating gas through said flow pipe, to a closed position, in which said shutter prevents said flow; - first thrust means configured to push said shutter into said closed position; - a retaining mechanism removably mounted in said valve body, suited to maintain said shutter in said open position and releasable to free said shutter; - release means suited to force the release of said retaining mechanism; - a control element removably mounted in said valve body, movable between a locking position to prevent said release of said retaining mechanism against the action of said release means and a released position to allow said release of said retaining mechanism; - a first actuator device suited to force said control element into said released position, said first actuator device comprising: - an actuator body equipped with a first end, said actuator body being movable between a rest position in which it allows said control element to maintain said locking position and a working position in which said first end forces said control element into said released position; - a retaining spring configured to force said actuator body into said rest position; - a shape memory spring configured to overcome the force of said retaining spring on said actuator body so as to force said actuator body into said working position when the temperature of said shape memory spring is within a predetermined temperature range; characterised in that said valve body comprises a through hole facing said control element, said first actuator device comprises a casing that houses said retaining spring and said shape memory spring and is equipped with a hole in which said actuator body is slidably mounted so that said first end protrudes outside said casing, there also being present connection means for removably connecting said casing to said valve body so that said first end is arranged through said through hole, wherein said first actuator device comprises a locking button slidably inserted in a through hole of said casing, configured to be able to act on said actuator body and equipped with a first end positioned outside of said casing and a second end associated with said actuator body in such a way that a movement of said locking button toward said actuator body causes a corresponding displacement of said actuator body into said working position. - a valve body which defines an inlet, an outlet and a flow pipe connecting said inlet to said outlet; - a shutter located in said flow pipe and movable between an open position, in which said shutter allows the flow of an operating gas through said flow pipe, to a closed position, in which said shutter prevents said flow; - first thrust means configured to push said shutter into said closed position; - a retaining mechanism removably mounted in said valve body, suited to maintain said shutter in said open position and releasable to free said shutter; - release means suited to force the release of said retaining mechanism; - a control element removably mounted in said valve body, movable between a locking position to prevent said release of said retaining mechanism against the action of said release means and a released position to allow said release of said retaining mechanism; - a first actuator device suited to force said control element into said released position, - an actuator body equipped with a first end, said actuator body being movable between a rest position in which it allows said control element to maintain said locking position and a working position in which said first end forces said control element into said released position; - a retaining spring configured to force said actuator body into said rest position; - a shape memory spring configured to overcome the force of said retaining spring on said actuator body so as to force said actuator body into said working position when the temperature of said shape memory spring is within a predetermined temperature range; characterised in that said valve body comprises a through hole facing said control element, said first actuator device comprises a casing that houses said retaining spring and said shape memory spring and is equipped with a hole in which said actuator body is slidably mounted so that said first end protrudes outside said casing, there also being present connection means for removably connecting said casing to said valve body so that said first end is arranged through said through hole, wherein said first actuator device comprises a locking button slidably inserted in a through hole of said casing, configured to be able to act on said actuator body and equipped with a first end positioned outside of said casing and a second end associated with said actuator body in such a way that a movement of said locking button toward said actuator body causes a corresponding displacement of said actuator body into said working position.