The most compromising and common issue we encounter is that plant noise data (fans in particular) never includes frequency signatures. Octave bands: yes. Narrow band (that defines if there is a tone): no. If there is a tone, in the UK it attracts a 6dB penalty – which only puts your predictions out by a factor of x4! Consequently, if you want to play safe, you over-engineer mitigation which adds a massive cost overhead. This is unacceptable. We try to get round this by asking for a smartphone recording from an installation anywhere in the world so we can design the optimum noise control measures.
This is a ridiculous state of affairs considering that you can do an accurate narrow band tonal analysis with a smartphone app for free. Noise consultants are also to blame as only a very small proportion of them carry out tonal analyses.