Upvote:3
First, I will assume that OP refers to the case of going over the top on an assault rather than engaging in a surreptitious raid across no-man's land.
Consider the assault on Vimy Ridge by the Canadian Corps over Easter Weekend, 1917. The assault was performed over 4 days by 15,000 men of the Canadian Corps, of whom nearly 3600 would die and over 7,000 more would be wounded. This gave a survival rate of about 76%, and a not-wounded rate of about 29%.
The odds during the earlier French and British assault on Vimy were worse.
Similarly, it is widely held that the survival rate of junior officers, those fools standing tall and exhorting the men to greater effort, was substantially worse than average.
Update:
It is argued below that my phrasing those fools above is inappropriate, as those individuals were merely brave. I disagree, and offer as evidence the definition of Foolhardy: recklessly bold or rash.
Any competent Allied commander in WWI should have known that the success of Britain and France during the Napoleonic Wars a century earlier had resulted from, respectively, steadfast defence under cover of a reverse slope, and bold skirmishing from covered terrain. The massed attacks engaged in from 1914 to 1918 by France and Britain bore no resemblance what-so-ever to successful Napoleonic tactics and would have had the same lack of success a century earlier as they actually demonstrated.