More than a dozen extra bomb squad officers are coming into Boston from New Jersey, New York, Connecticut, and New Hampshire. State Police have spent the last two days sealing manhole covers and removing trash bins, trying to close off any places where someone could hide a bomb. And there will be twice as many troopers as last year guarding the events around July 4 in Boston.
The measures are part of a stepped-up security effort being put in place for the city’s Independence Day spectacle, the biggest event to take place in Boston since the April 15 Marathon bombings.
The annual Fourth of July fireworks display brings up to a half-million people to the Esplanade, easily one of the biggest events in the city each year, and it was a potential target for the two suspects in the Marathon attack.
On Tuesday, troopers were loading trucks and trailers filled with bomb-detecting equipment to bring to the Hatch Shell, where the Boston Pops performs its Fourth of July concert.
Private companies have donated $2 million worth of robots, all-terrain vehicles, and thermal-imaging devices for bomb detection work. Thermo Fisher Scientific, a Waltham-based firm that specializes in laboratory instruments, loaned State Police $500,000 in products, including five handheld devices designed to help bomb squad officers figure out from a safe distance whether an unattended bag holds explosives.
“We bring a lot of state-of-the-art equipment to a lot of these events but this year is definitely a different environment,” said State Police Sergeant William Qualls of the bomb squad. “We feel prepared.”
There is no specific threat of terrorism by an organization or lone offender for the July 4 celebration, according to a 30-page safety assessment of the event prepared by several law enforcement groups, including the FBI.
But police had no information about a threat to the Boston Marathon either, before backpacks containing pressure-cooker bombs detonated, killing three people and injuring more than 260.
The safety assessment is an annual manual prepared for law enforcement officials assessing myriad potential threats.
For example, it instructs officials to question the credentials of people trying to enter secured areas.
It warns of would-be terrorists who could hide devices inside phony casts or their body cavities.
It also says police should be suspicious of food vendors and others who may have easy access around the Esplanade area.
“The use of part-time or temporary employees, as well as the large number of volunteers at many outdoor gatherings may limit the ability of event sponsors to background screen for all staff,” the report states. “This celebration is seen as one of the most prominent July 4th celebrations in the nation and it could represent an attractive symbolic target for terrorists.”
State Police said they do not yet know what the full cost of the extra security will be.
A spokesman declined to say how many troopers will be out in force.
State Police are primarily responsible for security around the Esplanade, though several other agencies, including Boston police, Cambridge police, and other smaller forces such as Everett and Quincy usually help patrol the event.
This year, 16 bomb technicians from out of state, including their dogs, will also help monitor the event, Qualls said.
But in the end, the eyes of the public will be the best weapon for law enforcement, said Jeffrey Addicott, director of the Center for Terrorism Law at St. Mary’s University in San Antonio.
“The first line of defense is the public,” he said. “If you see somebody put down a backpack next to you and walk away, say something. It’s just a matter of you being aware and taking responsibility for your safety.”
Authorities have announced that there will be new security checkpoints on the Esplanade and tough new bans that will prohibit visitors from carrying in backpacks, coolers on wheels, cans, glass containers, premixed beverages, liquids greater than 2 liters, or any sharp objects.
Boating traffic on the Charles River will be sharply limited as well.
For a shaken public, though, vigilance can easily veer into paranoia, said Lisa Fliegel, a Boston-based trauma counselor who has worked with survivors of the Marathon bombings, as well as victims of gun violence in Dorchester and terrorism in Israel and Northern Ireland.
“The first thing we want people to do is distinguish between paranoia and vigilance,” she said. “Paranoia is you start to think everybody around you is a bomber and vigilance is you’re playing close attention to everything.”
After police stopped the Boston bombing suspects, Tamerlan Tsarnaev, who was killed during a standoff with officers, and his brother, Dzhokhar, officials said the two men initially planned to set bombs off during the July 4 celebration.
“Even though the person who might have done it is caught and the other is dead we still feel that one of our icons is at risk,” Fliegel said.
Just knowing the Fourth of July celebration was a target of a terrorist is an emotional assault not only on the public, but also police, Fliegel said.
“I’m worried about law enforcement,” she said. “How are they going to be feeling when they’re guarding this event and everybody’s mind is under assault by the mere suggestion that something could have happened [on July 4]?”Maria Cramer can be reached at email@example.com. Follow her on Twitter @GlobeMCramer.