Sodium hydride decomposes certain solvents-violently.

An article in the American Chemical Society’s Chemical & Engineering News newsmagazine draws attention to the hazard posed by sodium hydride when used in certain polar aprotic solvents such as dimethylsulfoxide (DMSO) and dimethylformamide (DMF). Although these hazards have been known for fifty years, it appears that use of NaH with these solvents is common, judging from the large number of published syntheses that use them together. It is recommended that NaH not be used with polar aprotic solvents at all. See for more detail.