When has a cause of gas explosion, a Death toll smaller than 63, and a Location of penygraig?
CREATE TABLE "mining_disasters_in_the_rhondda_valley_1" (
  "colliery" text,
  "location" text,
  "date" text,
  "year" real,
  "death_toll" real,
  "cause" text
);
SELECT "date" FROM "mining_disasters_in_the_rhondda_valley_1" WHERE "cause"='gas explosion' AND "death_toll"<63 AND "location"='penygraig';