“So this,” says Ian Bell, in auspicious tones, “was the first inverted coaster – it hangs off the track, doesn’t ride on it – in the country. It’s not specially fast – 50 mph. Not particularly long either – 90 seconds. But it’s my favourite ride in the UK. It’s a work of art, in its way. A masterpiece.”

Nemesis, the Alton Towers rollercoaster before which we stand, has it all, Bell says: barrel roll, downwards helix, inline twist, vertical loop. Near-misses aplenty. It snakes in and out and around itself. It hugs the ground; plunges headlong into ravines; swoops wildly past waterfalls.

“It’s the intensity of the experience, the interaction with the terrain,” he says. “It feels like everything’s rushing at you, not that you’re rushing towards it. It’s … it’s just a world-class ride. Ninety seconds of sheer bliss.”

Bell (“Black polo, bald and a beard. Can’t miss me”) knows quite a bit about rollercoasters. He runs an enthusiasts’ website, coasterforce.com, dedicated to them, visits three theme parks a month – from Hong Kong to Dubai, Denmark to Florida, Blackpool to Drayton Manor – and reckons he’s ridden 700 rides at 200 venues in the past 10 years, most of them a lot more than once.

Scary? Not really. “There’s an element of scaring yourself that appeals,” he says, as we settle ourselves at the front of the ride train – as the carriage is known – and a Nemesis attendant pulls the restrainers down over our shoulders. “But you do it to be transported, really. To forget for a minute who you are. It’s an out-of-control experience in a safe environment.”

Except, you know, it isn’t always completely safe, is it? Ten days ago, on a ride called the Smiler in another part of the park, 16 people were hurt when their train slammed at high speed into a stationary, empty test car that had stalled on the track in front of them.

Four young people were badly injured: a 17-year-old girl had to have her left leg amputated, and her 18-year-old boyfriend suffered two broken knees. The park has accepted full responsibility, and both it and the HSE have launched investigations. A combination of human and mechanical error seems likely.

It was, though, very rare: freakishly, horribly, tragically unlikely. In all his rides, on all his travels, Bell says, as I take my glasses off and hand them to a red-shirted attendant (when hanging upside down on a fiendishly banked bend at 50mph, you can’t be sure of keeping them), he has never witnessed an accident, nor met anyone who has witnessed one.

“These things are incredibly safe,” he says. “Every ride is tested for 1,000 hours before it opens to the public. There’s regular servicing, an exhaustive annual inspection. They test run every ride at the beginning of every day, and whenever they add a train; there are computer checks, sensor checks, manual checks, visual checks before every ride. They’re safe.”

And it is indeed true that statistically, you are considerably more likely to be hurt on your way to a theme park than at one. In the US, where more than 300m people take 1.7bn rides at more than 400 theme and amusement parks every year, the chance of injury is one in 24m; injury rates for children’s buggies, golf carts and folding lawn chairs are higher.

But on a fine, early-summer day at Alton Towers this week – which, according to the Themed Entertainment Association, drew 2.6m visitors last year, up 3% on the previous year – there are, perhaps understandably, a few small managerial jitters. (There are also some in the front left-hand seat of Nemesis, which is now getting ready for launch.)

The Smiler and two other high-octane rides in the vicinity are shut; a children’s ride, the Octonauts Rollercoaster Adventure, has been evacuated after a visitor became upset; the park management issue a statement denying it had closed two further attractions after someone found a “big metal clip” under one of them.

Still, for the most part, the throng of visitors, at an adult on-the-day price of £50 (although a survey Bell did a while back found that, what with online booking, family tickets, season tickets, cereal-packet offers and the rest, barely 7% of theme park visitors pay full price), seem entirely sanguine.

“It’s awful what happened, of course, but it was incredibly unusual,” says Sophie Leeson, an accountant from Sheffield who is celebrating her 25th birthday with her boyfriend, Joe Jackson. “We did think twice about coming, but to be honest that was probably more because three of the best rides are shut. Oblivion and the Smiler closed … that’s a shame.”

Jackson confesses to feeling “a little bit more nervous, probably. I don’t think I’ll be sitting in the front row.” Liam Stott, from Manchester, says that, on balance, now might even be “a better time to visit: some people might be put off, you know? The place might not be so crowded. And the safety checks will certainly be good, you can bet on that. It’s the thrill, the adrenaline, though, isn’t it? Can’t beat it.”

So the aficionados say. I wouldn’t know. A confession: aside from a few childhood fairgrounds, this will be my first proper rollercoaster ride. Not out of any particular aversion; I just never really got around to it. No strong feelings one way or the other. Still, as the safety harness on Nemesis clicks into place, I become aware of a slight tension in my neck. A touch of clamminess in the palms.

Rollercoasters – or something vaguely like them – have been satisfying thrill-seekers like Stott since the 17th century, when the St Petersburg aristocracy enjoyed nothing more in wintertime than getting into a sled and throwing themselves down specially built 15-metre-high wooden ice slides.

In fact, rollercoasters are still known as “Russian mountains” in several countries, including France, where Les Montagnes Russes at Belleville and the Promenades Aériennes at the Parc Beaujon took the contraptions to the next level: both featured wheeled carriages securely anchored to a track.

By the 1840s, Paris reportedly also had the first vertical loop: a four-metre-high affair that carried one daring person at a time through a death-defying upside-down experience in a wheeled car, and which became known as a centrifugal railway (accident rates are not recorded, but the vertical loop did not return to widespread use until the 1970s).

In the US, meanwhile, a Pennsylvania mining company built the Mauch Chunk gravity railroad, a 14km downhill track originally used to deliver coal to the nearest township, but fairly soon converted – after the coal ran out – to carry 35,000 excited passengers a year, at 50 cents a pop.

The success of the scenic railway, as it later became known, prompted a number of designs – none of them ever built – for “improved inclined railways”, but it was a Sunday school teacher called LaMarcus Adna Thompson who got the “gravity pleasure ride” business out of the blocks: his Switchback Railway, constructed at Coney Island in 1884, paid for itself in just three weeks, charging a nickel a ride.

By 1888, Thompson had built nearly 50 rollercoasters around the US and Europe, patenting innovative technologies such as cables to pull the cars up the hill, and under-track triggers to halt the ride in an emergency.

Other entrepreneurs soon chimed in with continuous-loop (as opposed to one-way) tracks, spiralling helixes and – making a brief reappearance, until too many passengers complained of whiplash – vertical loops. By the early 1900s, rides were so fierce that people would pay just to watch them.

In 1912, a man called John Miller invented a game-changer: the under-friction wheel, which kept trains bolted to the track and solved the hitherto troubling matter of accidental derailment – at the same time allowing for ever more daring speeds, steeper plunges and wilder spirals.

At the height of rollercoasters’ golden age in the 1920s, the US alone had more than 1,500 of the things, some of them hitting speeds of 60mph. Several were nose-bleedingly vicious; one, the legendary Cyclone at Crystal Beach Park in Ontario, Canada, even employed its own registered nurse.

But the Great Depression took its toll, and by the 1960s the number of US coasters had fallen to just 200. Disneyland’s Matterhorn Bobsled, opened in 1959, sparked their modern-day renaissance, and for one simple reason: its tracks were made of steel, rather than wood. This was a smoother, quieter, safer and altogether less threatening ride.

“Steel just revolutionised the whole business,” says Bell. “You could now have far, far more intricate rides, many more twists and turns – corkscrews, rolls, finally even full vertical loops. It basically allowed track designers to be inventive.”

And inventive they certainly have been. Today’s top rides bear names such as Tower of Terror, Intimidator, Millennium Force, Mean Streak and Hades 360; The Beast, Goliath, Desperado and California Screamin’; The Boss, Cannibal, Untamed, Vertigorama and Speed: No Limits.

They boast a whole new vocabulary of features: interlocking loops, multiple inversions, standup trains, heartline rolls, cutback inversions, linear-launched trains, floorless trains, 90-degree (and more) vertical drops, pneumatic propulsion, flying coasters, vertical free-fall drops and so on.

Alton Towers’ ill-fated, £18m Smiler, notes Bell, was the first rollercoaster in the world to feature a stomach-pleasing 14 inversions. The world’s current fastest ride, Formula Rossa in Abu Dhabi, hits 140mph in five seconds, using a hydraulic launch system that generates a release velocity not far off that of the steam catapult on an aircraft carrier.

The current tallest rollercoaster, Kingda Ka at the Six Flags Great Adventure park in Jackson, New Jersey, “hits 120mph pretty much instantaneously, then takes you straight up for about 420 feet, then straight down again,” says Bell. “You queue for two-and-a-half hours, and it’s all over in about 10 seconds. But what a 10 seconds those are … ”

There are limits, of course, to what a rollercoaster can put a person through. Designers have to be careful that the G-forces a ride delivers do not exceed what the human body can take, and that the pace of the ride allows brains enough time to detect changes and adjust muscles.

Most rides, Bell said, aim for between four and six Gs for what is known as the positive vertical (which pushes you into your seat), and between one-and-a-half and two Gs for the negative vertical (which sends you flying out of it). The designer’s task, he notes succinctly, is “to thrill people without making them sick”.

Encouragingly, old-fashioned wood, in decline since the 1920s, is now making something of a comeback. There is a certain retro appeal to the clickety-clack of a straight wooden dipper, Bell reckons, and its less complicated physics offer purists an experience they crave – air time: “That moment when you reach the top of a rise and hang, weightless, stomach in mouth, before plunging down the other side. Magic.”

We are currently in the middle of a new rollercoaster golden age, he said: 171 new rides were opened around the world last year, the highest number ever. (There are 170 coasters in the UK; Bell has ridden 163 of them.)

Aficionados such as Bell suspect the relentless drive for the extreme but ultimately momentary thrill of ever higher, ever faster, ever taller may slowly be giving way to a trend towards rather more complex, lasting experiences. “These days, I tend to like the ground-huggers,” he said.

“There’s a great new ride called Helix at the Liseberg park in Sweden. It does 60mph, but it winds in and out of trees, around a hillside, leaps over and under stuff. It’s got a couple of corkscrews, a zero-G roll, a loop and an inline twist. But it’s just a really sustained, beautifully paced, totally rewarding experience. And it lasts two minutes.”

Something, in other words, a little like Nemesis, which we are now about to ride. For a first-timer, it is a somewhat intimidating prospect. But ride it I do, in the front row, with Bell grinning and yelling and gesticulating beside me all the way round, and I do sort of get it: the hair-on-end, cheek-rattling, stomach-disappearing, breath-depriving, stagger-inducing exhilaration of it, the companionable terror of hearing your fellow passengers screaming their lungs out.

“So are your legs wobbling?” asks Bell, solicitously. “If your legs aren’t wobbling, the coaster hasn’t done its job. You’ve got rollercoaster hair, though. That’s a good start.”

He leads me off to show me Rita, over on the other side of the park: 0-62mph in 2.8 seconds, he said. You gotta try it, you’ll love it. “Safe? It’s safe,” he says firmly. “I rode The Smiler six times and never felt unsafe once. Rollercoasters are incredibly safe.”

Faster, higher, loopier … rollercoaster records

Longest: Steel Dragon 2000, Nagashima Spa Land, Japan Built to celebrate the year of the dragon in 2000, this rollercoaster cost $52m, due to the extra steel required to make it earthquake-proof. The ride covers almost 2.5km and can carry 1,050 riders every hour.

Fastest: Formula Rossa, Ferrari World, United Arab Emirates Based on the world-famous Autodromo Nazionale Monza racetrack, the hydraulically launched rollercoaster reaches 149mph in five seconds. Riders must wear protective masks to avoid injury from collisions with insects and dust particles.

Longest drop: Kingda Ka, Six Flags Great Adventure, USA With its apex towering 139m above the ground, riders are launched through a 270° spiral during the descent, experiencing a moment of weightlessness before plummeting towards the ground. This stomach-churning ride lasts just 28 seconds.

Steepest: Takabisha, Fuji-Q Highland, Japan Under the shadow of Mount Fuji, the record-breaking 121° beyond-vertical drop sends riders into a terrifying freefall. Even so, the ride’s record is slender, with the Australian Green Lantern Coaster featuring a drop only half a degree gentler.

Tallest inversion: GateKeeper, Cedar Point, USA Hoping to capture the magic of flight, millions of visitors to Cedar Point amusement park have experienced the thrill of dangling 52m upside-down above the ground on this highly popular ride in Ohio.

Most loops: Smiler, Alton Towers, United Kingdom Comprising of a record 14 inversions, this £18m rollercoaster has been the subject of several safety concerns since opening in May 2013, but still proved popular with visitors to Alton Towers before the latest incident that led to its temporary closure. Patrick Greenfield