上午6時56分，廠區主管宣布廠區緊急狀態。30分鐘後，廠長Gary Miller宣布進入全面緊急狀態。大都會愛迪生公司（Met Ed）通知賓州緊急狀態管理局（PEMA）後，PEMA迅速通知了地方政府，賓州州長索伯格（Richard L. Thornburgh）。索伯格旋即指派副州長史堪頓（William Scranton III）負責處理三哩島事故。
工廠操作人員的不確定性反映在 Met Ed 向政府機構和媒體發表的零碎、模糊或矛盾的聲明中，特別是關於場外放射性釋放的可能性和嚴重性的聲明。斯克蘭頓舉行了一次新聞發布會，他在會議上對這種可能性進行了保證，但也令人困惑，他表示，儘管「有少量輻射釋放……正常輻射水平沒有增加」。這些說法與另一位官員和 Met Ed 的說法相矛盾，他們都聲稱沒有釋放任何放射性物質。事實上，工廠儀器和場外探測器的讀數已經檢測到放射性釋放，儘管其水平只要是暫時的，就不太可能威脅公眾健康，並且前提是保持對當時高度污染的反應器的遏制。
州政府官員對 Met Ed 在對工廠進行蒸汽排放之前沒有通知他們感到憤怒，並確信該公司淡化了事故的嚴重性，因此向 NRC 求助。在收到 Met Ed 的事故消息後，NRC 啟動了位於馬裡蘭州貝塞斯達的緊急應變總部，並將工作人員派往三哩島。 NRC 主席 Joseph Hendrie 和委員 Victor Gilinsky[56] 最初認為這起事故「令人擔憂，但不引起恐慌」。吉林斯基向記者和國會議員介紹了情況，並向白宮工作人員通報了情況，並於上午 10 點會見了另外兩名委員。然而，NRC 在獲取準確資訊方面面臨著與國家相同的問題，並且由於缺乏明確的指揮結構，也沒有權力告訴公用事業公司，在應對緊急情況時組織上準備不足，從而進一步受到阻礙。當地區域的疏散。
^Spiegelberg-Planer, Rejane. A Matter of Degree(PDF). IAEA Bulletin (Vienna, Austria: Division of Public Information, International Atomic Energy Agency). September 2009, 51 (1): 46 [October 16, 2021]Three Mile Island is mentioned on page 47
^The International Nuclear and Radiological Event Scale(PDF). INES. International Atomic Energy Agency. August 1, 2008 [October 16, 2021]. Level 5: Accident with Wider Consequences; Three Mile Island, USA, 1979 – Severe damage to the reactor core.
^Secondary system. U.S. Nuclear Regulatory Commission. March 9, 2021 [October 16, 2021]. The steam generator tubes, steam turbine, condenser, and associated pipes, pumps, and heaters used to convert the heat energy of the reactor coolant system into mechanical energy for electrical generation. Most commonly used in reference to pressurized water reactors.
^Primary system(PDF). Reactor Concepts Manual, Pressurized Water Reactor. USNRC Technical Training Center: 4-3. [October 16, 2021]. The primary system (also called the Reactor Coolant System) consists of the reactor vessel, the steam generators, the reactor coolant pumps, a pressurizer, and the connecting piping. A reactor coolant loop is a reactor coolant pump, a steam generator, and the piping that connects these components to the reactor vessel. The primary function of the reactor coolant system is to transfer the heat from the fuel to the steam generators. A second function is to contain any fission products that escape the fuel.
^Walker, J. Samuel. Three Mile Island: A Nuclear Crisis in Historical Perspective. Berkeley, California: University of California Press. 2004: 211 [October 19, 2021]. ISBN 0-520-23940-7（美国英语）. The commission concluded that Met Ed, GPU, Babcock & Wilcox, and the NRC shared responsibility for the shortcomings in operator training. Those inadequacies were compounded by design flaws that undermined the efforts of the plant staff to deal with the accident. They included the cacophony of undifferentiated alarms, the inconvenient arrangement of instruments and controls, and the absence of clear indicators either of levels of water in the pressure vessel or of the position of the stuck-open PORV.
^Hatch, Maureen C.; et al. Cancer near the Three Mile Island Nuclear Plant: Radiation Emissions. American Journal of Epidemiology. 1990, 132 (3): 397–412. PMID 2389745. doi:10.1093/oxfordjournals.aje.a115673.
^Levin, R. J. Incidence of thyroid cancer in residents surrounding the Three-Mile Island nuclear facility. Laryngoscope. 2008, 118 (4): 618–628. PMID 18300710. S2CID 27337295. doi:10.1097/MLG.0b013e3181613ad2. Thyroid cancer incidence has not increased in Dauphin County, the county in which TMI is located. York County demonstrated a trend toward increasing thyroid cancer incidence beginning in 1995, approximately 15 years after the TMI accident. Lancaster County showed a significant increase in thyroid cancer incidence beginning in 1990. These findings, however, do not provide a causal link to the TMI accident.
Holton, W. C. The Cleanup of Three Mile Island Unit 2 – A Technical History: 1979 to 1990. Palo Alto, California: EPRI (Electric Power Research Institute). September 1990 （美国英语）. (PDF)
Osif, Bonnie A.; Baratta, Anthony; Conkling, Thomas W. TMI 25 Years Later: The Three Mile Island Nuclear Power Plant Accident and Its Impact. Conkling. 2004. ISBN 978-0-271-02383-0.
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