2 Answers

Technically no.. But the Prez ordered it: In the US, the correct term for non nautical use is "half-staff". Whilst the term "half-mast" is commonly used colloquially in place of half-staff, US law and military tradition indicate that "half-mast" is generally reserved to usage aboard a ship, where flags are typically flown from masts.[19][20] However, this distinction not commonly made in international English, where the correct general term remains as "half-mast", regardless of application.
In the United States, the President can issue an executive order for the flag of the United States to be flown at half-staff upon the death of principal figures of the United States government, and others, as a mark of respect to their memory. When such an order is issued, all government buildings, offices, public schools and military bases are to fly their flags at half-staff. Under federal law (4 U.S.C. § 7(f)), the flags of states, cities, localities, and pennants of societies, shall never be placed above the flag of the United States; thus, all other flags also fly at half-staff when the U.S. flag has been ordered to fly at half-staff. It is important to note that there is no penalty for failure to comply with the above law as to enforce such a law would violate the First Amendment.
Governors of the several U.S. states or territories are authorized by federal law to order all U.S. and state flags in their jurisdiction flown at half-staff as a mark of respect for a former or current state official who has died, or for a member of the armed forces who has died in active duty. The governor's authority to issue the order is more restricted than the president's and does not include the discretion to issue the order for state residents who do not meet the criteria stated. Since a governor's executive order affects only his or her state, not the entire country, these orders are distinguished from presidential proclamations.
Under 4 U.S.C. § 7(m) and established traditions by Presidential proclamations, the flag of the United States is to be flown at half-staff in following circumstances:[21]
For thirty days after the death of a current or former president or president-elect, as occurred after the death of President Reagan and the death of President Ford.
For ten days after the death of a current vice president, current or retired chief justice, or current speaker of the House of Representatives.
From the day of death until interment of an Associate Justice of the Supreme Court, a secretary of an executive or military department, a former vice president, the President Pro Tempore of the Senate,[22] or the governor of a state, territory, or possession.
On the day of death and the following day for a Member of Congress.
On Memorial Day until noon.
Upon presidential proclamation, which has recently included: the interment of Frank Buckles,[23] the death of Senator Ted Kennedy,[24] the remembrance of the 9/11 attacks,[25] the death of Pope John Paul II,[26] the Space Shuttle Columbia disaster in 2003,[27] the victims of Hurricane Katrina,[28] the Indian Ocean earthquake and tsunami,[29] the deaths of Coretta Scott King[30] and Rosa Parks,[31] the Virginia Tech massacre,[32] the Fort Hood massacre,[33] the funeral of Neil Armstrong,[34] the death of Libyan Ambassador Chris Stephens, the 2012 shooting in Aurora Colorado, the 2012 Sandy Hook Elementary School shooting, the 2013 Boston Marathon bombings.[35] and the 2013 Washington D.C Navy Yard shooting
Federal law requires the flag be flown at half-staff on Peace Officers Memorial Day (May 15), unless that day is also Armed Forces Day. Yearly presidential proclamations also mandate that the flag be flown at half-staff on Pearl Harbor Remembrance Day (December 7),[36] and Patriot Day (September 11).[37]
On October 16, 2001, President George W. Bush approved legislation requiring the United States flag to be lowered to half-staff on all Federal buildings to memorialize fallen firefighters. Pub.L. 107–51 requires this action to occur annually in conjunction with observance of the National Fallen Firefighters Memorial Service.[38] The date of the National Fallen Firefighters Memorial Service is traditionally the first Sunday in October. It is held at the National Fallen Firefighters Memorial in Emmitsburg, MD.[39]
4 U.S.C. § 7(m) was modified with new legislation signed into effect on June 29, 2007, by President Bush, requiring any federal facility within a region, which proclaims half-staff to honor a member of the U.S. Armed Forces who died on active duty, to follow the half-staff proclamation.

Flags lowered for 19 dead firefighters.  This was in the town where the fire station was located. See the article here:  http://www.katu.com/news/national/We-just-lost-19-of-the-finest-people-youll-ever-meet-Arizona-wildfire-firefighters-213829471.html  I don’t know why the nation didn’t lover their flags…………..