Eugene Kelly (54), whose teenage brother Robert was killed in the fire in 1981, said: "It was disgraceful and very irresponsible to put a bomb in a park where children play. They just didn't give a damn.
"Little kids could have gone to see what was in the package and could have picked it up.
"It would have been innocent people again who suffer. I don't know what's wrong with the world," he said.
He added the leaving of the viable pipebomb in the Coolock park was also very disrespectful to the memory of all the young people from the area who died in the blaze. Gertrude Barrett, whose son Michael was killed in the tragedy, also condemned the placing of the viable explosive device in the park.
"An awful lot of people use the park. It's quite vast and anyone could have been injured or worse. I absolutely condemn it. There's a children's playground in the park, too.
"It's terrible. I remember a report about a child who picked up one of those bombs and he lost all his fingers. It's dreadful," she said.
Gardai called in army bomb experts after the device was found around 7pm on New Year's Eve. An army spokesperson told the Herald: "The device was dismantled at the scene and was handed over to gardai for further investigation."
Sources say that the pipe bomb was left in the park so that it could be collected at a later stage. Tensions have been high between rival factions in the Coolock area since last September's murder of Real IRA terror boss Alan Ryan in nearby Clongriffin.
There have been at least two pipe bomb attacks organised by dissident Republicans against innocent people who have no links to the gangs that organised Ryan's murder.
Gardai have been working on the theory that 'Mr Big' and a veteran Tiger Kidnap criminal, who mentored the gangster, planned the murder of Alan Ryan after their gang became entangled in a bitter feud with the rival outfit which kicked off after a nightclub assault just over a year ago.
'Mr Big' -- who comes from a respectable middle class background and is well educated -- has been striking fear into the underworld for years.
His stronghold is in the Coolock, Darndale and Donaghmede areas of the capital.
In response to the increase in pipe bomb tensions in the Coolock area, gardai have mounted a number of special operations targeting gangs that have been making the bombs for dissident Republicans.
A number of garda searches have focused on a halting site at Northern Cross in Darndale which has been raided at least four times in recent months.