Everything is fine

If you are at home when the attack does not take place because it cannot take place because everything is OK, do not attempt to leave. In particular do not come into physical contact with any persons, especially government employees, who will be busy ensuring that everything is fine, as doubtless it will be. They perform this duty most effectively while still in possession of their epidermis. Also do not touch the water supply, which is also fine.

Loss of eyesight is temporary and will cease to be a problem within six to eight minutes of exposure, or ten to twelve minutes for those of a hardy constitution. The government suggest passing the intervening time putting your affairs in order or writing a will, in Braille. This is nothing to worry about, and a simple look around you, without leaving the building, will reveal that your neighbours are doing exactly the same thing. Some of them may also be resting, perhaps slumped on the pavement or hanging out of car windows. Rest is important when faced with no risk of a disfiguring and prolonged death.

There's more over at Rum and Monkey, explaining just why there is no pressing need to panic.