An actuator comprising: a cylinder having an axial dimension; a piston axially movable within the cylinder with the cylinder having an upper and lower end which is sealed around the piston; a piston rod extending at a lower end of the piston and having one end connectable to an operator; a cavity occupying a space within the cylinder between the upper and lower ends, through which space the piston travels, an axial dimension of the piston extending through the space within the cavity when the piston is in a first position of its travel, the axial dimension of the piston having at least two separate diameters with a largest of the diameters leading a smaller of the diameters in a direction of travel of the piston to move the piston to a second position, the two diameters occupying at least a portion of the space when the piston is in the first position; a material occupying at least a portion of the space within the cavity, the material expanding upon an increase in temperature to exert a force on the piston that causes the piston to move to the second position when the material rises above a preselected temperature; and characterized by: a safety lock configured to prevent the piston from moving from the first position to the second position when the material is substantially below the preselected temperature and free the piston to move in a direction toward the second position when the material rises approximately above the preselected temperature. a cylinder having an axial dimension; a piston axially movable within the cylinder with the cylinder having an upper and lower end which is sealed around the piston; a piston rod extending at a lower end of the piston and having one end connectable to an operator; a cavity occupying a space within the cylinder between the upper and lower ends, through which space the piston travels, an axial dimension of the piston extending through the space within the cavity when the piston is in a first position of its travel, the axial dimension of the piston having at least two separate diameters with a largest of the diameters leading a smaller of the diameters in a direction of travel of the piston to move the piston to a second position, the two diameters occupying at least a portion of the space when the piston is in the first position; a material occupying at least a portion of the space within the cavity, the material expanding upon an increase in temperature to exert a force on the piston that causes the piston to move to the second position when the material rises above a preselected temperature; and characterized by: a safety lock configured to prevent the piston from moving from the first position to the second position when the material is substantially below the preselected temperature and free the piston to move in a direction toward the second position when the material rises approximately above the preselected temperature. a safety lock configured to prevent the piston from moving from the first position to the second position when the material is substantially below the preselected temperature and free the piston to move in a direction toward the second position when the material rises approximately above the preselected temperature.