Stephen and Alan Harris were working at a housing estate
Stephen Harris, 34, of Monasterboice Road in Crumlin, Dublin, lost his fight for life in Beaumont Hospital at 9am today.
He was caught up in the same suspected methane gas incident which claimed the life of his brother, Alan Harris, a father of two, on Wednesday.
The pair had been inspecting underground pipes on a housing estate in the Portmarnock area of north Dublin.
Alan Harris, in his 40s, was the owner of DrainTech, a company specialising in drainage clearance and pipe and sewer unblocking in the Dublin region for about 20 years.
The accident happened on the Drumnigh Woods estate in Portmarnock.
The brothers were beginning to assess work on pipes under the road, some of which were reported to be 20ft (6m) below the surface.
Stephen Harris, who was knocked unconscious by the noxious gases, was rescued by fire crews but lost his fight for life in hospital.
His family requested that their privacy be respected during their grief.
Investigations by the Garda and the Health and Safety Authority are continuing.
Comment: Methane is a colorless, odorless gas at room temperature and standard pressure, and as residents 'complained of a smell' prompting the sewer inspection, this tragedy could be related to inhalation of other toxic 'sewer gases'. Such as hydrogen sulfide, which does have an odor and is "heavier than air, very poisonous, corrosive, flammable, and explosive".
In India last week, three workers died after inhaling poisonous gases inside a manhole. Those working on sewer systems or living in 'low-lying areas' may be particularly susceptible to such 'heavier than air' out gassing.
Such seeps are likely to be contributing to increased manhole explosions worldwide, and to fish die offs, such as the "catastrophic" one elsewhere in Ireland recently.