On November 29, 2016, Northstar Materials, Inc., an indirect subsidiary of MDU Resources Group, Inc., received an imminent danger order issued by the Mine Safety and Health Administration under section 107(a) of the Federal Mine Safety and Health Act of 1977. The imminent danger order was issued at the State Option Pit in Hubbard County, Minnesota, upon observation of two miners working on the discharge end of an aggregate crusher without adequate fall protection. The equipment they were working from was additionally not locked out or blocked out against motion. Upon observation the miners came down from the equipment, thereby terminating the order. The miners had been trained in the use of fall protection and harnesses were available to them; however, the miners were not wearing harnesses at the time of the citation. The company has written procedures regarding lock out of equipment, which were not followed by the miners at the time of the citation.

This Form 8-K was not filed within 4 business days after receipt of the imminent danger order because field personnel did not follow company procedure, which requires prompt internal reporting. The company has taken additional measures to correct this reporting lapse and ensure information that is reportable under Item 1.04 of Form 8-K will be reported in a timely manner.

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About MDU Resources Group, Inc. (NYSE:MDU)

MDU Resources Group, Inc. is a diversified natural resource company. The Company’s segments include Electric, Natural Gas Distribution, Pipeline and Midstream, Construction Materials and Contracting, Construction Services and Refining. Montana-Dakota Utilities Co. (Montana-Dakota) is a public utility division of the Company. Montana-Dakota, through the electric and natural gas distribution segments, generates, transmits and distributes electricity and distributes natural gas in Montana, North Dakota, South Dakota and Wyoming. The Company, through Cascade Natural Gas Corporation (Cascade) distributes natural gas in Oregon and Washington. The Company, through Intermountain Gas Company (Intermountain) distributes natural gas in Idaho. Great Plains Natural Gas Co. (Great Plains) is a public utility division of the Company. Great Plains distributes natural gas in western Minnesota and southeastern North Dakota.

MDU Resources Group, Inc. (NYSE:MDU) Recent Trading Information

MDU Resources Group, Inc. (NYSE:MDU) closed its last trading session down -0.62 at 29.00 with 1,085,818 shares trading hands.