Earlier this summer, a wildfire near Yarnell, Ariz., killed 19 firefighters and destroyed 109 homes at an estimated cost of $6.8 million. When Gov. Jan Brewer asked President Barack Obama to declare a federal disaster, he turned her down.

The Yarnell Fire began on Jun. 28, 2013 from a lightning strike and was approximately 1.5 miles from Yarnell, AZ when this photo by the US Forest Service photo was taken.

A few months earlier, a fertilizer plant explosion leveled the town of West, Texas. In that case, Obama did declare a disaster — albeit after an appeal from Texas Gov. Rick Perry. After Hurricane Sandy rocked the eastern U.S. last October, the feds declared landlocked West Virginia and several other states to be disaster areas — but not Florida.

The Federal Emergency Management Agency (FEMA) is supposed to follow specific guidelines when it advises the president on whether to approve federal disaster aid for a state or individuals.

But experts in the field say the disaster standards are unclear — and often ignored. The result is that disaster decisions can seem arbitrary or politically motivated.  FEMA’s public explanations typically do not shed much light on its rulings, leaving governors to wonder why they missed out on federal help.

“The damage to uninsured private residences from this event was not of such severity and magnitude as to be beyond the capabilities of the state, affected local governments and voluntary agencies,” Craig Fugate, FEMA administrator, wrote to Brewer in a typical denial.

Between 1991 and 2011, presidents approved more than 85 percent of governors’ disaster requests. During that period, the states most likely to be denied disaster declarations were Connecticut (39 percent), Arizona (37 percent), Texas (35 percent) and Rhode Island (33 percent), according to a Stateline analysis of documents obtained under the federal Freedom of Information Act.

Disappointed governors may see politics at work when their requests fall flat, but the numbers tell a different story. According to Stateline’s analysis, Democratic presidents denied requests from Republican governors 53 times and Democratic governors 44 times. Republican presidents turned down requests from fellow Republicans 49 times and from Democrats 43 times. Republicans held the majority of governorships between 1995 and 2007, and again after the 2010 elections.