A high integrity protection system includes a flow line including an inlet configured to be connected to a first source of pressure and an outlet configured to be connected to a downstream system. A first subsystem is installed on the flow line between the inlet and the outlet. A second subsystem is installed on the flow line between the inlet and the outlet, and the second subsystem is in a parallel flow configuration in relation to the first subsystem. The system includes a second source of pressure configured to be fluidically connected to the first subsystem and the second subsystem.