How is it different from technical grade?
AFAIK lab/technical grade SN means it's been tested so the impurities (the other 1%) are known. After all, if you're using it to conduct experiments in a lab, it's important to know what the other 1% was (heavy metals, bacteria, etc) and how they might affect your experiments.
Food grade usually means that the impurities haven't been tested, or are unknown, or they're negligible to the point where it doesn't matter for "general non-lab use" (e.g. curing meats).
That's why either is fine to CTB, but if it didn't come in a sealed container by the manufacturer, do a nitrite test before using it (to verify it's purity and that it's sodium
nitrite and not sodium
nitrate)