If wildfires are dangerous to humans why are some set intentionally by forest rangers?

Yes, wildfires are dangerous but there are fires intentionally set by forest officials. They actually do it on purpose. The two types of forest fires set are called prescribed or controlled burn.

In both of these method, fire can burn unwanted plants making more space for appropriate trees to grow. It can also save trees from insect infestations and other invasive plant species. 

after a more than a decade and a half of combating al qaeda (aq) in afghanistan and pakistan,

the united states faces a diverse array of threats from al qaeda affiliates in the middle east and

africa. while senior al qaeda figures reportedly remain based in pakistan, the network includes

a number of affiliates across the middle east and africa including al qaeda in the arabian

peninsula (aqap), al qaeda in the islamic maghreb (aqim), and al shabaab. al qaeda also

retains a small but possibly growing presence in afghanistan. u.s. officials have stated that al

qaeda still maintains a foothold in syria through its ties to hay’at tahrir al sham (formerly

known as the nusra front), though the exact nature of that relationship may be evolving. this

report examines the threat posed by al qaeda affiliates in the middle east and africa as described

by u.s. officials and outside observers, as well as the u.s. approach to date in responding to these

threats. this was all i could find hope this : )