F. He thought that the puddle was about 100 square feet in area, and perhaps half an inch deep, on average. Rob's formaldehyde puddle evaporation scenario. He had responded to quite a few formaldehyde spills, and he had never encountered a boiling puddle of formaldehyde. Instead, he had observed that formaldehyde puddles don't boil, but instead evaporate slowly, much as a pool of water would do.
Pure formaldehyde is a gas at room temperature and atmospheric pressure.
However, it's very unusual to encounter formaldehyde in its pure state. Instead, it is available commercially as a solution of formaldehyde in water. The boiling point of formaldehyde in solution depends on the percentage of formaldehyde present, but is much higher than typical ambient temperatures. The answer has to do with the difficulty of modeling solutions and mixtures. It's much harder to model a mixture or solution than to model pure chemicals because it's difficult to accurately predict properties such as vapor pressure for solutions or mixtures.