From the HJC website:
Helmet Replacement (All Models)
Although your HJC Helmet is constructed with the best materials available to offer a long-lasting product, it will eventually need to be replaced. Immediately replace your helmet if:
• It has suffered an impact. Your helmet is only designed for ONE impact. An impact may fracture the outer shell or compress the impact absorbing liner. You may not be able to detect this damage. Any impact in a crash or a drop from as low as 4 feet is enough to damage your helmet.
• The shell, lining, or retention system is damaged. The helmet shell, the impact absorbing lining, and the retention system must be in good condition to provide you with the most protection.
Even if your helmet has not been damaged, it needs to be replaced every 3 to 5 years depending on how much you use it. Over time, UV rays and adhesive and component aging will damage your helmet. Wearing a damaged helmet may increase your risk of serious injury or death in an accident.
If you are unsure if you need to replace your helmet, contact HJC America before using your helmet again.
Using Your Helmet Correctly
To reduce the risk of serious injury or death and to help prevent damage to your helmet:
• Never adjust your helmet accessories while riding – Only make helmet adjustments when stopped.
• Never drop your helmet – Dropping your helmet may crack the shell or damage the protective foam. The damage may not be visible. Your helmet is only designed for ONE impact. Refer to "Helmet Replacement for more information on what to do after helmet has been dropped.
• Never wear anything between your head and your helmet – This may reduce the effectiveness of your helmet.
• Never hang or hook your helmet on anything including mirror stalks, handle bar, or sissy bars – Doing so may cause damage to the helmet protective foam or liner.
• Never use insect repellent on or around your helmet – Insect repellant may damage your helmet’s visor, shell, protective foam, or other components.
• Never expose helmet to gasoline or gasoline fumes – Gasoline may damage your helmet’s visor, shell, protective foam, or other components.
- If you have any questions on what other substances may damage your helmet, please email us at [email protected]
That being said, I have dropped helmets then continued to use them for years without incedent, then again I could just be lucky.
Sorry to hear about your run in with gravity.