Considering the chemical constituents and the active ingredients of most hair sprays, you would require a solvent to remove hair spray. A solvent is usually a liquid substance that has the ability to dissolve certain types of solids, as in this case some of the compounds of dried hair spray residue. This is a technique that is borrowed from a household technique of removing hair spray residue that settles on surfaces in your bathroom. Once you finish removing the hair spray, however, you would need to immediately attend to your hair because the solvent will also wash out all the natural hair oil secretions and it may even irritate your scalp if left in for too long.
Hair spray is made up of compounds like polyvinylpyrrolidone and polydimethylsiloxane. When these two are mixed together they have the ability to stiffen up the hair. However, these have to be sprayed out of a container and this requires the use of a solvent. During the most popular period of hair spray, the most common solvent that was used to spray anything out of a can was chlorofluorocarbons. Nowadays, the solvents that are used are alcohol based. Alcohol is therefore the key to removing the residue. For this, you can take any household alcohol like vodka, whisky, or a similar strong spirit. Pour a substantial quantity into a bowl and then wash your hair in it until the hair spray comes off. After that, wash with water to remove any trace of the alcohol in your hair. If necessary, you can also shampoo your hair. This treatment will leave your hair very dry and devoid of natural skin oils. You will need to replenish the lost oils by using almond oil. Simply dip your fingers in some almond oil and run your fingers through your hair. After that, comb it for a smoother application. You would obviously not be in a condition to step out of the house after this but if you must, try and wait for an hour before washing your hair in pure water only. Towel it and then step out. You could wash after you get back.
Ideally, you should try to avoid using too many chemicals on your hair and, if inevitable, you should only use them sparingly. Even heat treatments like hot irons and curling irons should only be used once every two days to avoid too much damage to the hair.