At about 3pm on the last Monday in April 1986, a mass of black clouds unleashed a sudden downpour on the sleepy western Russian town of Novozybkov, sending participants in a rehearsal for that year's May Day parade running for cover.
The wind was strong, and the rain an unusually torrential, 40-minute downpour, but Sergei Sizov, a professor at the local teacher-training college, thought nothing of it until delivering a lesson the next day on one of the more outlandish responsibilities of educators in the Soviet Union - detecting and responding to nuclear and chemical attack.
"The class was called 'nuclear and chemical reconnaissance', and it basically involved showing [students] how to use a military grade Geiger counter," he said. "It was just something everyone was meant to know, like stripping a Kalashnikov."
But instead of registering the expected trace of background radiation, the dial surged to levels Sizov had only seen in text books about nuclear attack.
Alarmed and confused, he immediately called the local civil protection headquarters.
"All they said was 'that's impossible'. They didn't know anything about it."
As it turned out, it was worse than possible. Three days earlier, on Saturday, April 26, 1986, the nuclear power station at Chernobyl, just over 160km away in what is now Ukraine, had exploded in one of the worst nuclear accidents in history. That Monday's rainstorm was exactly the kind of disaster that Sizov's training had been designed to detect.
Nestled on the border where Russia, Belarus, and Ukraine meet, the marshy birch forests and vast, flat fields of Novozybkovsky district in the Bryansk region are about as close as you can get to the heart of old Russia.
A traditional stronghold of the Old Believers, an often persecuted Orthodox sect that adheres to older interpretations of the liturgy, it is a place where storks nest atop telegraph poles and much of the population, speaking a mixture of all three countries' languages, still lives in villages of hand-built wooden houses and depends on subsistence farming and the local forests for survival.
In spring, it is almost idyllic. But residents face serious dangers from long-term exposure to gamma rays from Caesium 137 and beta-emitting Stronium 90 that has affected at least three generations.
Today, at least 120,000 to 200,000 people continue to live in badly contaminated parts of Bryansk region, said Alexei Kiselyev, a radiation safety adviser with Greenpeace Russia.
"Radiation is not what it was, of course. Immediately after the accident, the area around the village of Svyatsk was registering 5 micro-sieverts per hour. Now it is down to about two," he said.
"Belarussian estimates say this area will be unfit for human habitation until the year 2176. Until then, it should be considered an exclusion zone."
Russia's Ministry of Emergency Situations considers any background radiation level above 0.8 microsieverts per hour hazardous for its workers, and any level over 0.6 microsieverts per hour unsafe for local populations.
Outside the Svyatsk resettlement zone, rates are generally lower, but still hazardous. On a trip with Greenpeace Russia, the Telegraph found multiple spots in inhabited areas outside the Svyatsk zone displaying readings of up to 0.7 microsieverts, and up to 0.9 in woodlands where people gather birch sap.
The effects are believed to include a spike in cancers, especially of the thyroid, stomach and lungs, and unusually high rates of cerebral palsy, Down's syndrome, and physical disfigurement that continue to affect newborn children.
Galina Velichenko was 11 years old when the deadly rain fell on Novozybkov. She doesn't remember that day, but she does remember watching the May Day parade that went ahead, as if nothing had happened, just days afterwards.
She appeared to be unaffected. But when Denis, her second son, was born in 2000 with curvature of the spine, undeveloped ears, and a host of other physical disabilities, she realised that exposure at the time combined with years of consuming local foods had had an impact. Her father-in-law died from lung cancer, also recognised as linked to Chernobyl.
As a victim of Chernobyl fallout, Denis received eight free operations to restore his hearing and ears and relatively generous state benefits, although some entitlements - like specialist education, rehabilitation classes, and trips to sanatoriums on the Black Sea - have had to be fought for. Charities have paid for crucial equipment including a hearing aid.
After the Chernobyl accident, Soviet authorities moved to evacuate the worst affected parts of the region. An especially contaminated zone on the Belarussian border was resettled and the village of Svyatsk, a centre of the Old Believer faith and home to over 1000 people in 1986, was demolished to discourage people returning.
An early plan to evacuate all 40,000 people from Novozybkov itself was abandoned in the face of protests by residents unwilling to be uprooted, but a cleanup ordered by Boris Yeltsin proved largely effective. Initially one of the worst contaminated areas, the bulk of the town now registers normal levels of background radiation.
However, the clean-up did not extend far into the countryside, and many people in polluted areas outside the Svyatsk zone either declined resettlement, or were pulled back by homesickness, lack of employment, and a frosty reception from people in other parts of the country fearful of the "Chernobylovtsy".
Natalia Kundik, a councillor and librarian in the village of Stary Bobovychy, just outside the Svyatsk resettlement zone, is under no illusions. She has lost her mother and a colleague at the village library to cancer, and later discovered that the family home, which was incomplete and lacking a roof during the rains of April 1986, was more radioactive inside then out. But economic pressures leave many with a choice between starving today or accepting an increased risk of cancer later, she said.
Pensioners live on little more than 11,000 roubles ($220) a month, and many unskilled workers earn little more. "What can you do? You have to live," said Valentina Lomonosova, 52, whose 7-year-old granddaughter has just been diagnosed with cancer. She supplements her wages with a veritable small holding including eight rabbits, a dozen hens, and a pig called Vasya. Like many others here, she also continues to gather mushrooms, berries, and birch sap from the forest. "It's probably radioactive, but it's tasty," she joked.
She wasn't wrong. Tests on a jar of her pickled mushrooms at the Novozybkov sanitary laboratory showed they contained concentrations of 867 Becquerels per kilogram - well above the official safe limit of 500 Bq/kg. A dry batch taken from another village tested at the same time showed 109,000 Bq/kg (dry mushrooms have a higher safe limit of 2,500 Bq/kg).
Yet, even here, a deep-seated insouciance was remarkable. "We recommend against consuming these mushrooms," said the lab director. Asked if she would eat them herself, however, she admitted she would ignore official advice. "Of course. They're tasty," she said.
Despite the apparent resignation of many people to radiation, poverty has made many here sensitive about the government compensation for those affected. Last October, Dmitry Medvedev, the Russian Prime Minister, signed a decree reclassifying several areas, including Novozybkov and Stary Bobovychy, as areas of lower risk.
Based on soil-sample analysis carried out on behalf of the ministry of emergency situations, the move officially reflects the gradual decline of radioactivity over the past three decades, but it also comes with a consequent cut in monthly benefits.
All they said was 'that's impossible'. They didn't know anything about it.
Mothers of Novozybkov, a campaign group, argue that the analysis failed to take into account the patchiness of radiation - meaning a single soil sample from one village could easily miss hot spots just metres away.
The Russian Supreme Court recently rejected a challenge to the decree by more than 50 plaintiffs, including Kundik. She says the group are awaiting the court's written statement explaining its reasoning, before they begin a second challenge.
Kiselyev would like to see a proper exclusion zone put in place around Svyatsk, as he says not enough has been done to understand the long-term impacts.
"It's 30 years since the accident, and the fact is, there's still far too much we don't know about Chernobyl," he said.