Acesulfame potassium, also known as Acesulfame K or Ace-K, is one of six non-nutritive sweeteners and one of five artificial sweeteners approved by the FDA. The name is derived from its components acetoacetic acid and potassium, which forms a highly stable and crystalline compound similar to saccharin. Unlike aspartame, which may break down at a particular temperature, the high stability of Ace-K makes it useful to sweeten baked items.  It is the fourth oldest sugar substitute – preceded by saccharin, cyclamate, & aspartame – to gain FDA approval, dating back to its discovery in 1967 by Karl Clauss & Harald Jensen.
It all started in 1967 when Clauss, one of two – the other being Jensen – Hoechst A.G. scientists in Frankfort, Germany, dipped his fingers into the chemicals he was working with by accident. In the same way aspartame was discovered, Clauss licked his fingers to pick up a piece of paper and noticed a sweet taste. In 1978, the World Health Organization gave it the generic name Acesulfame Potassium.  The sweetener is listed as being approximately 200 times sweeter than sucrose with, “a clean, quickly perceptible, sweet taste that does not linger or leave an aftertaste.”  However, some list high doses of Ace-K as having a bitter taste. 
It is known as having a synergistic effect when used together with other sweeteners, such as aspartame, to enhance and sustain the desirable sweet taste in foods and beverages. It does not provide calories because it passes through the body without being metabolized and is excreted in the urine while remaining unchanged. 
Ace-K received approval around the globe from 1983 until 2000, gaining FDA approval in 1988. The FDA approved acesulfame K for use in soft drinks on July 6, 1998. In 2003, the FDA gave Ace-K a general purpose approval – meaning Ace-K can be used in any product.  It is used in, “thousands of foods, beverages, oral hygiene and pharmaceutical products in about 90 countries. Among these are tabletop sweeteners, desserts, puddings, baked goods, soft drinks, candies and canned foods.”  The current ADI set by the FDA for Ace-K is 15 mg/kg of body weight per day, which has an equivalence of 30 to 32 cans of diet lemon-lime soda sweetened with Ace-K. 
The “amount of potassium in acesulfame potassium is extremely small. A packet of tabletop sweetener containing acesulfame potassium has just 10 mg of potassium. In comparison, most individuals receive approximately 2,000 to 3,000 mg of potassium from various foods every day. For example, a banana contains 400 mg; an orange 252 mg; and a sweet potato 390 mg of potassium.” 
The safety of Ace-K, like other artificial sweeteners, has been questioned by the general public. One example of complaints includes the use of methylene chloride, a carcinogenic compound, during the manufacture of Ace-K. “Methylene chloride is used as a solvent, which otherwise is used in other commercial applications like paint stripper, degreaser and propellant gas. Its use in the food industry is contentious, and exposure to this chemical compound over a prolonged period of time can result in headaches, liver complications, mental confusion, cancerous developments, visual impairment and renal diseases. In some medical conditions, it has been observed that people tend to suffer from allergic reactions, nausea induced vomiting, depression, intense headaches, and liver diseases too.”  Further hazards indicate that methylene chloride, “may result in the development of cancerous cells. Research on rats has revealed that it may result in lung and breast cancer.” It is also stated that Ace-K hampers the ability of the body to metabolize other food products. 
Tests of Ace-K carried out in the 1970’s – two on rats, one on mice – were listed as inadequate to establish lack of carcinogenicity with some of the following reasons: [source]
Subchronic tests were not conducted for the rats and mice used in the tests on which the FAPs rested
It is likely the minimum toxic dose/maximum tolerated dose (MTD) was not achieved in the rat and mouse studies
Randomization of test groups was not carried out properly
Mice were held on test for only 80 weeks, rather than the 104 weeks characteristic of National Toxicology Program (NTP) bioassays
Animal husbandry and monitoring of animals on test were evidently poor, as indicated by high disease rates in the animals and extensive autolysis of tissues.
The idea that Ace-K is a carcinogen, or leads to health hazards, has not been scientifically proven. But like other artificial sweeteners, there is no scientific certainty that Ace-K is not a carcinogen and carries no health hazards. Use at your own risk.