Secret Soviet Space Casualties

Think that the U.S. space program is risky?

Think again. The Soviets lost 48 people in just one incident.

(Excerpt)

On March 18, 1980, 48 technicians died at Russia's Plesetsk Cosmodrome when a Vostok booster exploded while being fueled. An investigation later revealed that the substitution of lead-based for tin-based solder in hydrogen peroxide filters had resulted in the breakdown of the hydrogen peroxide and the resulting explosion. The incident was reported to the general public only in 1989, almost ten years later, in the era of 'glasnost'.

Source: Shadows of the Soviet Space Age.

See also Jame's Oberg's "Dead Cosmonauts".