A "certified packing" (as suggested by itascot) may help, but for sure is not enough if the requirement to fulfill is compliance to ISO 15848-1 standard: that is a qualification of the valve design (not of a single component) and may be achieved only by type-testing fully assembled valves (mock-up fixtures, for example, are clearly excluded by the standard...).
On the other hand, in order to qualify the stem packing itself, as a stand-alone component, other standards exist, like API 622, for instance: about this issue, see also thread408-253784 within this Forum.
Regards, 'NGL