When cold LNG comes in contact with warmer air, it becomes a visible vapour cloud. As it continues to get warmer, the vapour cloud becomes lighter than air and rises. When LNG vapour mixes with air it is only flammable if it’s within 5%-15% natural gas in air. If it’s less than five percent natural gas in air, there is not enough natural gas in the air to burn. If it’s more than 15 percent natural gas in air, there is too much gas in the air and not enough oxygen for it to burn.