Spall

The fan had been bolted to the roof of the tunnel since 2011, and for fourteen
years it did nothing at all.

At ten to eight on a March morning it comes down onto a car in the nearside
lane. The driving examiner in the passenger seat is killed. The seventeen-year-
old at the wheel, eleven minutes into her first driving test, survives by the
width of a car.

Everybody says the concrete. The Haverscar Tunnel is forty-six years old, it
sits in salt air off the North Sea, and every road tunnel in the country sheds
concrete off its own face. It has a name - spalling - and a budget code, and
nobody investigates it, in the same way that nobody investigates the weather.

Ada Marram reads broken metal for a living. Hired by the contractor who needs
this to be somebody else's fault, she finds that the concrete held. All four
steel anchors failed, and they failed in fatigue - which takes years, and takes
hundreds of thousands of load cycles.

The control system says that fan was started eleven thousand times.

The fracture surface says four hundred thousand.

And the bands across the metal are not a smear of ordinary wear. They are
fifty-one separate visits, each one a night's work, going back further than the
tunnel's own records survive - and somebody was standing at the control panel
five hours before a man died.

She has no client, no warrant and no authority. She has a tunnel carrying
thirty-one thousand vehicles a day, twenty-two more fans hanging over the
carriageway, and no way of telling anybody which one is next.

SPALL is the second Factor of Safety thriller. The engineering is real and
checkable, and that is the point of the series.