Ignore drain traps at your peril

While the recent Quincy house blast proved newsworthy by its rarity and triggered investigative activity by sanitation experts, police, and FBI agents, it was also a startling reminder to many that potential danger lurks along any sewer or septic tank drain. Almost no one likes to think about sewerage and drain traps, but everyone should, especially families with young children. And more people should know that only water-filled traps keep volatile and pathogenic gas away from living and working spaces.

Legal scholars still argue about definitions. Sewers are covered ditches or drains typically found in cities. The urbanity of sewers originates in novelty. Not until after the Civil War did even large cities have sewers. Until then almost every building had its own cesspool that had to be emptied more or less frequently. Increased use of piped drinking water paradoxically increased the spread of disease, since more water caused cesspools to overflow.

While ``ditch" and ``drain" have no precise legal meaning in the United States, ``drain" now indicates long-abandoned rural ditches that carried sewage downhill into swamps and rivers. In suburbs, ``drain" designates the pipe that connects private indoor piping to a septic tank or municipal sewer. Only when two private drains merge into a larger jointly owned pipe does that pipe become a sewer.

No one expects sewerage to be clean. Contamination from cesspools, septic tanks, and sewers may come from water contact, especially backflow that fills basements with raw sewage and germs, and from infiltration of noxious, dangerous gases. In 1775, Englishman Alexander Cummings patented the first so-called S trap that used two sliding valves to stop both water and gas from rising through a toilet bowl. Americans patented valve-free but more effective S traps only seven years later.

While the traps have vague S shapes, often with the S almost horizontal, the initial indicates their early name, ``stink" traps. In the years before anyone understood the germ theory of disease, most inventors hoped to stop foul-smelling miasmas from making entire buildings almost uninhabitable. Since most toilets emptied straight down to cesspools, few inventors worried about fluid backflow.

Building city sewer systems in the 1880s and 1890s posed new problems for sanitary and civil engineers and for plumbers. Many homeowners thought sewers were an excellent idea for neighbors, but not for themselves. They feared flooding, especially after rain, and they worried that industrial waste might swamp basements. Homeowners argued that they understood how to maintain their own cesspools and knew more or less what material went down their own drains. Sewers might carry dangerous chemicals from distant factories.

In 1921, only 1 percent of US houses had both electricity and indoor plumbing. The first national plumbing code originated in 1928, after Secretary of Commerce Herbert Hoover insisted that industry experts do something to avoid an incipient public health disaster.

Plumbers confronted almost insurmountable difficulties in retrofitting old houses with indoor plumbing. Not until 1890 did an engineer, Robert Manning, devise formulas to calculate the flow of water and solid wastes along sloping drains. Steeply angled drain pipes flushed water so quickly that solid material scarcely moved, and quickly blocked drains. But smells wafting up from sink and bathtub drains, angled and vertical, slowly enraged the American public.

A farmer approached a small-time Wisconsin manufacturer of farm equipment late in the 19th century with an odd idea. He wanted John Michael Kohler to heat a large, combination horse drinking trough/pig scalder to 1,700 degrees Fahrenheit, sprinkle it with enamel powder, and see if it might make a large, classy bathtub. The experiment worked, the farmer paid Kohler a cow and 14 chickens, and the manufacturing firm suddenly had a wonderful new product.

But the snazzy enameled bathtubs atop claw-footed legs drained massive amounts of water into still-primitive drain systems, sometimes sending water or odors up other drains in the house.

In 1874 a handful of smart plumbers gathered together to solve one plumbing problem involving a retrofitted toilet that produced horrible odors. Bit by bit they figured out that the air pressure had to be the same on each side of the water-filled S trap, lest suction now and then empty the trap and allow gas to rise from the drain. They connected vent pipes to drains, and ran the pipes upward through roofs so foul-smelling gases would dissipate.

They promulgated their idea in trade journals, and then through the early versions of the organization now known as the Plumbing, Heating, and Cooling Contractors National Association. By 1930 plumbers installed odor-free, backflow-free home drainage systems according to codes rigorously enforced not only by licensed experts but also by plumbing inspectors.

Sewer gas can be many separate gases. Hydrogen sulfide smells like rotten eggs and can injure eyes and lungs. Above 300 parts per million, it can kill. While it and ammonia, which harms the eyes and respiratory tract, warn people away through severe, distinctive smell, methane and carbon monoxide are odorless. Both produce flu-like symptoms if breathed for long in any amount, but methane kills instantly, too. It explodes.

Methane has a low flash point and explodes in low concentrations given some weather and other conditions. It is the swamp gas that exploded spontaneously in south-of-Boston swamps in Colonial times, giving rise to the will-o-the-wisp tales.

In confined spaces, especially basements, it does far more than flare. When a furnace or other electric motor switches on, the tiny spark ignites the methane that can tear apart a house.

Methane is so dangerous that plumbers never vent drains into chimneys, or place rooftop vent pipes near chimney tops. One spark can fire the methane, and the blast can run downward through the vent pipe.

In the Quincy blast, officials suspect that the water in the S trap of a long-disused basement toilet dried out, opening the path for some explosive vapor into the home.

Investigators have not yet found the source of the flammable cleaning fluid they suspect vaporized and exploded, nor do they know whether chemicals harmless in themselves met beyond private drains and reacted in a common sewer to make something incredibly dangerous as it wafted up a private drain.

Plumbing is not for amateurs, and never has been.

In any building, especially old structures with plumbing components used infrequently and connected to a sewer, licensed plumbers provide the only expertise useful in evaluating extremely serious potential danger.

Norwell resident John Stilgoe is Orchard Professor in the History of Landscape at Harvard University.