Susan Guest, 30, of Downend, Avon, died in hospital six weeks later. A month before she died, her son Franklin was born by caesarian section, weighing 3lb.
Mrs Guest poured the methylated spirits on to charcoal embers in a barbecue in the family back garden on 18 July, the coroner was told.
There was an explosion and her clothes caught fire as her children, Karina, four, and Calvin, one, watched from a playpen.
In a statement, fire officer Randolph Pearson said it was likely that a vapour cloud from the methylated spirits had been ignited by the embers.
The inquest heard that a neighbour, Richard Kembery, rushed to Mrs Guest's aid on hearing her scream. He found her trying to telephone for help, having doused the flames in her children's paddling pool. An ambulance arrived 20 minutes later.
Mrs Guest was taken to Frenchay Hospital in Bristol for treatment to burns on her arms, legs, neck and back. Her husband, John, 38, was with her when she died six weeks after the accident.
The coroner said she died from pneumonia due to severe burns and recorded a verdict of accidental death, describing it as 'appalling, horrific and tragic'.