danger作“危险”、“风险”讲时，是不可数名词；作“危险的人；危险因素；危害；威胁”讲时是可数名词；作“（坏事或不快之事发生的）可能性，危险”讲时，既是可数也不可数，要从具体的语境当中看。

danger的用法

1.不可数名词 danger of sth.危险；风险

（1）Danger! Keep Out!

危险！请勿入内！

（2）Children's lives are in danger every time they cross this road.

孩子们每次过这条马路都面临着生命危险。

（3）Doctors said she is now out of danger (= not likely to die) .

医生说她已脱离危险。

2.可数&不可数名词danger of sth./danger that（坏事或不快之事发生的）可能性，危险

（1）There is no danger of a bush fire now.

目前不存在野外大火的危险。

（2）The building is in danger of collapsing.

这栋建筑有垮塌的危险。

（3）How many factory workers are in danger of losing their jobs?

有多少产业工人可能失业？

（4）There is a danger that the political disorder of the past will return.

昔日的政治动乱可能会重演。

3.可数名词danger to sb./sth. 危险的人；危险因素；危害；威胁

（1）Smoking is a serious danger to health.

吸烟严重危害健康。

（2）Police said the man was a danger to the public.

警方说该名男子对公众是个危险。

（3）the hidden dangers in your home

家里潜在的危险因素