There is a common misconception about the Boil Release that of Mei Terumi. Many people say that it can not be used in open areas and only in enclosed spaces, but i will attempt to disprove this.
Mei can use Hidden Mist Style as well as the Acid Mist. When she has used her Hidden Mist, she has used it in open spaces and it has worked. This is also shown again when Zabuza fought Team Kakashi. The Hidden Mist style worked in an open area and obscured vision. Now onto Boil release which is nearly identical to Hidden Mist however it is acidic in nature. If Mei can successfully use Hidden Mist in a open environment, then surely she can use Boil release in a open environment although it will not be as effective. If Zabuza can affect the environment in such a way that it obscures vision, i am confident that Mei can too with Hidden Mist and her Boil Release.
Why do people think she can not use it in open areas? For one, against Sasuke she enclosed the room to use it against him. This does not necessarily mean that it has to be used this way, it is just more effective.
Also, when Mei deactivated the jutsu when a hole had been created in the room does not show us it could not be used in open areas as the reason why it was deactivated was to PROTECT THE KAGE etc. Otherwise, they would have been affected by it.
Why hasn't Mei used Boil release in open areas? Because she has never fought by herself. She has always fought with team mates and using the acid mist will harm them as well as the opponent.
Now onto it's uses in battle. Mei could potentially combine the Acid Mist and Hidden Mist to, firstly obscure the opponent's vision and also to keep them away from herself otherwise they would be affected by the acidity.
To conclude, Mei's acid mist can most likely be used in open areas as well as enclosed areas, due to Hidden Mist working in open areas etc.
Mei can use Hidden Mist Style as well as the Acid Mist. When she has used her Hidden Mist, she has used it in open spaces and it has worked. This is also shown again when Zabuza fought Team Kakashi. The Hidden Mist style worked in an open area and obscured vision. Now onto Boil release which is nearly identical to Hidden Mist however it is acidic in nature. If Mei can successfully use Hidden Mist in a open environment, then surely she can use Boil release in a open environment although it will not be as effective. If Zabuza can affect the environment in such a way that it obscures vision, i am confident that Mei can too with Hidden Mist and her Boil Release.
Why do people think she can not use it in open areas? For one, against Sasuke she enclosed the room to use it against him. This does not necessarily mean that it has to be used this way, it is just more effective.
Also, when Mei deactivated the jutsu when a hole had been created in the room does not show us it could not be used in open areas as the reason why it was deactivated was to PROTECT THE KAGE etc. Otherwise, they would have been affected by it.
Why hasn't Mei used Boil release in open areas? Because she has never fought by herself. She has always fought with team mates and using the acid mist will harm them as well as the opponent.
Now onto it's uses in battle. Mei could potentially combine the Acid Mist and Hidden Mist to, firstly obscure the opponent's vision and also to keep them away from herself otherwise they would be affected by the acidity.
To conclude, Mei's acid mist can most likely be used in open areas as well as enclosed areas, due to Hidden Mist working in open areas etc.