"So the bomb ship is over that way, is it?" asks 81-year-old Margate resident Pat Smith, squinting out towards the Dover Strait. All we can see, from the plastic-paned windows of our promenade shelter, is the rain slicing sideways into choppy grey waves.

But somewhere out there in the squall bobs the Ruby, a Maltese-flagged cargo ship carrying twenty thousand tonnes of potentially explosive ammonium nitrate fertiliser that set off from Russia in July.

This is seven times the quantity of the same substance, I tell Pat, that wreaked havoc in Beirut in the summer of 2020, when a major explosion in the city's port caused at least 218 deaths, 7,000 injuries, and $15 billion in property damage, as well as leaving an estimated 300,000 people homeless.

She just nods. "Thing is, love, we have explosions all the time here in Kent." She reminds me that "they keep finding bombs from the war in the sea here anyway". Only two months ago a huge plume of brine was sent skywards when bomb disposal experts detonated an old mine which fishermen found just up the coast at Herne Bay.

I encounter the young, hipster version of Pat's indifference at the Turner Contemporary Gallery just up the prom.

"The military are always testing missiles here," a staff member explains, looking out casually towards the horizon through walls of the glass cube building. "They send those bombs into the sea here from Essex. Our desks shake. The walls shake. It's a reliable kind of thunder. A bit annoying but you get used to it. This Ruby ship just sounds like more of the same, right?"

Throughout the few hours I spend in Margate, I struggle to find anybody concerned about the floating could-be bomb anchored on the town's horizon. "Will it take out the seagulls if it blows?" questions one local. But most people just raise their palms and crack on with their days.

A few are more worried, however. In the Barnacle pub, Richard Martin, 62, tells me that the community Facebook group has been keeping an eye on their potentially explosive visitor. He sinks his half pint and scrolls through the 143 comments on a post about the ship. Some are jokes - "don't light up tonight!" and "send it up the Thames to the Houses of Parliament!" - but others see locals debating its presence offshore.

Former Royal Navy serviceman John Patterson warns his neighbours that this is "the same ship that was ordered out of Tromso Norway last week. Norway had the right idea. To top it up it's got damage to its rudder and hull as it ran aground as it left Russia with cargo and is trying to seek a port to have repairs done. It's trying to head back to Malta where it comes from."

The rumours of damage are true. The ship does appear to have been damaged in a storm after leaving Russia. Norway's Maritime Authority told the BBC the vessel was inspected by DNV Group, a leading organisation in maritime risk assessment and certification, to ensure it met safety and environmental standards. Though the group found damage to the vessel's hull, propeller and rudder, the Ruby was still deemed "seaworthy". But the DNV Group, and the Maltese flag registry, insisted that a "precautionary" tug escort the vessel for the remainder of its journey.

The ship was bound for Klaipeda, in Lithuania, according to ship tracking firm MarineTraffic. But the BBC reported it was denied entry to Klaipeda "because of its cargo". Its current destination is listed as Marsaxlokk, in Malta.

At Margate's RNLI shop the staff admit that they're concerned. "If that cargo explodes, then what happens here? Does the explosion cause some sort of tsunami that wipes us all out? Or is it just another big bang we'll forget about?"

"If the ship detonates, no doubt you'll get a big wave," says Andrea Sella, a Professor of Chemistry at UCL. "Beirut is the key example of that with one medium sized boat being dumped onto the dock. But it's the pressure wave above the water that does the real damage miles away, at the very least blowing out windows and in some cases bringing whole buildings down. That said, if they don't burn the ship, the risk of such a disaster is pretty low."

The national maritime emergency service has said it will monitor the ship's progress as it heads through UK waters, with vessels not permitted to seek permission from authorities to do so, provided their purpose is legitimate.

Sella concedes that there are "plenty of concerns" about ammonium nitrate (a major component of the explosive ANFO) because of its "rather disastrous history". But he doesn't believe Margate residents should evacuate in a panic.

"Ammonium nitrate is produced in the tens of millions of tonnes each year, and is shipped round the world because it is so widely used as a component of fertiliser. And then there's its use as an industrial explosive, normally mixed with diesel. So there are large quantities being moved around all the time. This stuff will be pure."

The explosion in Beirut, Sella argues, was down to "poor storage - it was left for years in a warehouse. And then the warehouse was also used to store fireworks. I cannot think of a more lethal combination since all of the ammonium nitrate incidents have been initiated by a fire of some kind - at high temperature, ammonium nitrate decomposes to gaseous products and how rapidly that happens determines the kind of bang that you'll get.

"The explosions in Tianjin [in northern China in 2015] were similarly initiated by poor storage alongside highly flammable materials, including cylinders of acetylene. In Waco [Texas, in 2013] too, a fire in a fertiliser storage facility led to an explosion that caused severe damage to nearby housing and a school."

Professor Sella believes that the Ruby's consignment is "probably at fairly low risk of explosion". What about the risk of spillage? "Not a major problem," he says. "Unlike an oil spill, the material is not toxic. Think of it like fertiliser - obviously 20,000 tonnes of fertiliser spilled in one place could be bad local news, and you might get serious local disruption from algal blooms, I suspect. It dissolves in water and washes away, so in a sense you'd end up with a similar problem to the issue of nitrogen fertiliser waste that washes off agricultural land but just much more localised.It leads to unwanted algal growth and certain bacteria will convert it to nitrous oxide which is a greenhouse gas. But these are not acute short-term problems.

"The issue of dumping too much nitrogen fertiliser onto land, is unquestionably a contributor to the large greenhouse footprint of agriculture."

Sella isn't an expert on how ammonium nitrate is transported. But he explains that the product is "produced as prills, little pellets that pour rather easily".

"These might - I'm speculating - be poured into large polyester-type bags that can be lifted by a crane, several hundred kilos at a time and then stacked either in containers or on pallets. If these lie around and the materials are warmed and cooled and subjected to moisture they can compact quite significantly into a big rock [which was one of the problems in Oppau and also in Beirut]."

It seems likely that the ammonium nitrate being shipped will be relatively new so probably not caked. "But it would be interesting to know what the nature of the repairs might be as clearly welding might significantly raise the potential fire risk," says Sella. "Some have suggested that the ship should be returned to port, but towing a ship back round the top of Norway sounds challenging, and the weather and sailing conditions aren't going to improve."

With these caveats in place, Sella has reassuring news for the seemingly blasé inhabitants of Margate. He thinks that barring a blaze on board, "the cargo isn't going to do very much". So Pat can eat her chips in peace. Although she is right to wonder where the ship and its cargo will end up. Sella suspects the Ruby's owners would "probably be wise to think seriously about off-loading the material without bringing it into port. Who will pay for it becomes a rather interesting question, as is the question of the extent to which Malta will take its responsibility as the nominal home country."

Meanwhile back in Margate, a seagull finishes Pat's chips. "Hope you stay on land and don't get caught up in any big bangs out there," she nods, affectionately, at the bird. "Oh, we'll all be fine!"