Abstract: The present invention relates to a safety valve for a containment (16) comprising a tubular body composed of a main branch (11) and a secondary branch (12) connected to said main branch (11) and opening into it via an aperture in the side of said main branch, a piston (13) mounted so that it slides inside said main branch (11) to free the said lateral aperture from the main branch, an upper stop (14) and a lower stop (15) both mounted inside the main branch and limiting the upward and downward displacement of said piston (13), the lower section of said main branch (11) being subject to a reference pressure, wherein an additional safety apparatus (25) is positioned under the tubular body between the lower section of said main branch and said reference pressure such that the maximum safety throughput rate of which the valve is capable is released in the event of an incident.