CSS: Background not showing up iPhone or iPad but works on iMac ( Safari )

I've got a full width hero background that is working properly on every browser we tested except for Safari on iPhone and iPad. It does work on iMac Safari. On iPhone and iPad it doesn't appear. Here's the code:

.hero {

margin: 0;

padding: 0;

height: 600px;

background-image: url('../images/heroFullScreen.jpg');

background-attachment: fixed;

background-position: center;

background-repeat: no-repeat;

background-size: cover;

}

You can view the site here: sanitonplastic.ca to recreate the problem if you've got one of the devices.

Really hope someone can help, we're supposed to be going live tomorrow.

Thank you!