Doha - World Athletics Championships organisers delayed the start time of the women's 20km race walk on Sunday as Doha's heat and humidity again triggered concerns for athlete safety.
A day after dozens of exhausted runners failed to finish the women's marathon as brutal conditions took their toll, officials said the women's 20km scheduled to start at 11.30pm (20:30 GMT) on Sunday would now get under way at 11.59pm instead.
The International Association of Athletics Federations (IAAF) said in a statement the move had been made in "consideration of the predicted weather conditions for the scheduled start."
"The IAAF Medical Delegate analysed all available information on the likely temperatures and humidity and recommended a half-hour delay to the start to attain the best possible conditions for athletes during the race," the statement said.
The IAAF said the forecast WetBulb Globe Temperature -- a measure of the heat stress which combines temperature, humidity, wind speed and other factors -- was expected to be 28 degrees Celsius (82 Fahrenheit) at the new start time.
The bulk of events in Doha are taking place inside the climate-controlled confines of the Khalifa Stadium, where a state-of-the-art air-conditioning systems maintains a comfortable temperature of around 23 degrees for athletes and spectators.
But marathon runners and endurance athletes however have been left to battle through the challenging combination of heat and humidity alone, stoking safety fears and drawing criticism from athletes.
The start times for all of the outside events have been shifted to around midnight in order to shield athletes from the worst of the heat in Doha, where daytime temperatures can reach 40 degrees.
However not even a start just a minute before midnight on Friday could prevent chaos at the women's marathon, where 28 of the 68-strong field fell by the wayside as the sauna-like conditions decimated the field.
Thirty athletes required medical attention while "a small number" were kept under observation. One athlete was referred to hospital, the IAAF said.
IAAF President Sebastian Coe has defended the sport's governing body over the weather issue, insisting that athlete safety is paramount.
The organisers point to larger than usual teams of paramedics on hand and an abundance of water and refreshment stations along the courses for the walking and marathon events.
"The overwhelming thrust of this is the welfare of the athletes," Coe said.
However for athletes toiling away in the conditions, the opening marathon was a grim experience.
Canada's Lyndsay Tessier, 41, admitted after the race she had been unnerved by the spectacle of so many fellow competitors wilting.
"You see somebody down on the course and it's just, extremely grounding and scary," said Tessier, who finished ninth.
"That could be you in the next kilometre, the next 500 meters."
Other athletes have been more forthright in their criticism of the IAAF.
France's defending 50km race walk champion Yohann Diniz was scathing of the IAAF's decision to award the championships to Doha, saying walkers and marathon runners had been treated like "guinea pigs" by the governing body.
Diniz, who dropped out early in Saturday's 50km race after complaining of "suffocating", said on the eve of the race he was "disgusted" by the conditions.
"I am extremely upset," Diniz said. "If we were in the stadium we would have normal conditions, between 24-25 degrees, but outside they have placed us in a furnace, which is just not possible."
French decathlon star Kevin Mayer, who will compete in the relative cool of the Khalifa Stadium, also condemned the IAAF, accusing the body of putting athletes "in jeopardy."
"Even if people aren't saying it out loud, it's obvious it's a catastrophe," he said.
"We saw about 30 people drop out of the marathon. It's sad."