OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at https://www.osha.gov.

November 6, 1980


THRU:               JOHN MILES
                    ACTING FIELD COORDINATOR

                    AND STATE PROGRAMS

SUBJECT:            Unique, Drilling Rig-Doghouses, Oil and Gas
                    Drilling Industries

A recent fatality in the Oil and Gas Drilling Industry has revealed the possible existence of serious hazards in a unique type of doghouse rig. This rig was manufactured by B & G Fabricators of Lafayette, Louisiana, and consists of a doghouse which is attached to and folds within a water tank. When the rig is operational, the doghouse is positioned above the water tank on floor plates laid across the water tank.

In one instance, the doghouse fell into the water tank and no one was injured. The manufacturer then retrofitted the rig with a cable across the tank which attached to threaded eye-bolts and it was tightened (brought taunt) by nuts on the eye-bolts. Another subsequent incident occurred on June 25, 1980, in Des Moines, New Mexico (inland Drilling Company) which resulted in one fatality and one injury when the doghouse collapsed during rigging down operations. The deceased was removing the cable in the water tank (retrofit cable), when it collapsed. The exact cause of the inadvertent collapse is unknown, but design flaws noted by the reporting office are:

First, there is no positive latch once the doghouse is in the upright position. The design relies on floor plates laid across the water tank, bridging the tank, and impeding the fore and aft motion of the doghouse. These floor plates apparently lodge in a grove across each end of the doghouse.

Secondly, there is no safety stop beneath the doghouse in the original design. After one experience of having the doghouse fall into the tank (no injuries) the employer retrofitted a cable across the tank attached to threaded eye-bolts, and brought taunt by running up the nuts on the eye-bolts from outside the water tanks.

Finally, movement of the doghouse in and out of its surrounding water tank is partially controlled by a wire rope sling attached to a fitting at the bottom of the tank, and reeved through a sheave mounted at the top center of one end of the water tank. This equipment, as supplied by the manufacturer, allowed a maximum wire rope diameter of 5/8-inch. Expert opinion indicates that this sling should be a minimum of 1-inch diameter wire rope with properly utilized end fittings.

Field experience had shown this sling to be inadequate, and an operating procedure was adopted which required that a line from a gin-pole truck be connected to an eye welded to the top of the doghouse. This line was not connected at the time of the accident.

There are approximately 22 rigs of this type known to be in existence and they are primarily located in New Mexico and Texas. No drawings, plans or specifications are available on this type of rig; therefore, such rigs should be thoroughly evaluated during inspections and appropriate action taken.

Copies of all citations and supporting evaluations/information should be sent to the Division of Occupational Safety Programming via the Acting Field Coordinator.