Final answer:
In the event of a chemical explosion, the most crucial first aid step is to rinse the affected teenager's face and eyes with water for no less than 15 minutes to dilute any chemicals, followed by immediate medical attention.
Step-by-step explanation:
If a chemistry experiment has blown up in a teenager's face, the immediate step prior to seeking medical care is to rinse his face and eyes with water for at least 15 minutes. This immediate dilution of the chemicals is critical to prevent further injury and to minimize damage to the eyes and skin.
Using a salt solution or other substances without knowing the chemical involved could potentially react with the contaminant and worsen the situation. Do not apply any creams such as petroleum or other substances as they may trap chemicals against the skin, and identify the chemical if possible, but do not delay initial flushing with water while doing so.
After thorough rinsing, seeking professional medical care is essential, especially if there is any ongoing pain, visual disturbance, or other concerns.