They knew to some extent about (b) when what's now the Tate Modern was built, but regulation was relatively weak until the 1950s, so there was nothing stopping

They knew to some extent about (b) when what's now the Tate Modern was built, but regulation was relatively weak until the 1950s, so there was nothing stopping them building it. _Knowing_ there's a problem is insufficient; making rules based on problems is required.