Firearm officers swooped in on a pub in St Albans following reports of a man with a samurai sword.
Hertfordshire Constabulary were called at 5.48pm on Saturday, February 9 to reports of an altercation in Spencer Street, St Albans.
A man was allegedly carrying a samurai sword and banging on the door of a property.
He was then reportedly seen with a baseball bat a short time later.
An unknown substance, believed to be boiling water, was thrown on the male along with a female victim.
An ambulance attended and the woman was taken to hospital with burns to her arm.
The sword was located by officers and the man was arrested in The Peahen public house shortly after 6pm, after allegedly attempting to dispose of the baseball bat.
He was taken to hospital with burns to the chest, face and neck area.
The incident followed an alleged disagreement between the suspect and a man known to the female victim earlier on the same day.
The man was reportedly assaulted by the suspect, sustaining a split lip and bruising to the forehead.
A 36-year-old man from St Albans was arrested on suspicion of causing grievous bodily harm, using violence to secure entry and criminal damage.
He was released on conditional bail until March 12 while enquiries continue.