tert-butyl hydroperoxide is potentially dangerous, but explosions are rare.
A solution of tert-butyl hydroperoxide and water with a concentration of greater than 90% is forbidden to be shipped according to US Department of Transportation Hazardous Materials Table 49 CFR 172.101.
In some sources it also has an NFPA 704 rating of 4 for health, 4 for flammability, 4 for reactivity and is a potent oxidant, however other sources claim lower ratings of 3-2-2 or 1-4-4.