The city Buildings Department is turning a blind eye to safety by allowing unlicensed or unqualified laborers to perform gas piping work in new or reconstructed developments, an explosive lawsuit filed by the plumbers union claims.

The Manhattan Supreme Court suit accuses the DOB of failing to comply with a city law that tightened up licensing requirements for gas piping installation following deadly explosions in East Harlem and the East Village in 2014 and 2015.

“DOB’s complete dereliction of its duty to enforce gas and welder qualification requirements has facilitated wholesale non-compliance with these safety rules throughout the City and created a public safety time bomb,” claims the suit, filed by Plumbers Union Local 1.

The 2020 law imposed restrictions on who can perform such hazardous “gas work,” making it illegal to do so without a DOB-issued Gas Qualification permit.

But the 45-page complaint cites examples alleging DOB approved of illegal gas work on taxpayer funded public projects, unlicensed workers performing piping installations and cases of “unverified inspections” by contractors.

Licensed union plumbers provided affidavits as part of the legal action, claiming they witnessed shoddy workmanship being performed in buildings and other workers without a “gas qualification” license.

The union claims the DOB is turning a blind eye while granting hundreds of gas approvals in large residential towers, schools, luxury hotels and other buildings, according to the suit.

It identifies at least 21 jobs where it alleges gas welders were not licensed, were unqualified or lacked documentation with the DOB. Those include the recently opened Ritz-Carlton New York Nomad Hotel in Manhattan, as well as the Mary Mount School at 115 East 97th Street and 7 Hanover Square/100 Pearl Street.

Local 1 trains and certifies pipe welders at its training facility in Queens, and their members do much of the gas line installations.

DOB regularly approves the pipework and authorizes the gas to be turned on – even when it knows that unqualified welders performed the work or was aware the contractor had not submitted any of the legally required documentation establishing that a qualified, certified welder was on the job, the suit charges.

DOB approved at least 460 gas authorizations from Nov. 19 to Nov. 30 last  year that did not contain any supporting documentation the work was performed by qualified vendors, according to the suit.

The union provided documentation alleging that two contractors — A&M Warshaw Plumbing & Heating Inc. and Donato Inc. Plumbing & Heating (“Donato”) –were using unqualified welders and submitting inaccurate information to DOB in support of gas requests.

It identified 31 approvals for Warshaw and 42 for Donato since January 2021 where the contractor either submitted no required documentation or identified an unqualified welder employed and assigned gas work.

The union similarly identified unlawful gas approvals for two other alleged violators for the same period — 44 for Demar Mechanical and 24 for TT Mechanical over the past four months, according to the suit.

Three affidavits provided by union welders claimed that the gas line work at 7 Hanover Square/100 Pearl Street was done by other subcontractors that was substandard or involved other workers without gas permit qualifications.

The suit says the DOB — despite prior complaints of violations over lack of licensing –allowed the firm Donato and a worker to do welding on the gas pipes and line at the recently opened 44-story, 250-room Ritz-Carlton. The building includes several luxury suites priced at nearly $10,000 per night, has luxury apartments for sale, a rooftop bar, a 7,000-foot spa, a restaurant and other amenities.

The union also accused DOB of approving “illegal gas work” on two taxpayer-funded public projects, Chestnut Common at 110 Dinsmore Place in Cypress Hills/East New York and Rockaway Village Apartments at 1725 Village Lane in Far Rockaway, by allowing welders do the jobs who “do not possess gas qualifications,” the suit states. The work at both sites was performed by Demar Mechanical Inc.

“To me this smells like a case of really bad gas,” Michael Apuzzo, business manager for Plumbers Union Local 1 based in New York City said in a statement to The Post.

The suit, which names the DOB and its acting Commissioner Kasimir Vilenchik as defendants, notes there have been four gas explosions reported in city buildings since February 2021.

“Given the damage caused by these gas explosions, the magnitude of the catastrophe that would result from a gas explosion in a 45-story tower in Manhattan, on a densely populated block, is incalculable,” the suit states.

The union urged the court to force DOB to enforce the city’s mandatory gas qualification and safety requirements.

DOB insisted it is enforcing the gas hook-up codes.