According to the Taiwan Labor Safety and Health Installation Regulation, confined space is defined as a space that has restricted access and inadequate nature ventilation for clean air, and is not intended for routine work. However, the size of the space is not specified.

The hand-hole and man-hole for electricity utility, both were constructed underground but different in size and depth, fit in the nature of confined space. Herein, a total of 322 hand-holes of three types (640, 810 and 1650) were measured for oxygen, hydrogen sulfide, carbon monoxide and flammable gas using a direct-reading instrument.

The results indicate that 8.3%, 1.6% and 3.6% (overall mean of 3.4%) of the hand-holes measured had minimal oxygen level less than 18%. Such anoxia condition is hazardous to workers if ventilation is insufficient or lack of proper air supply. The other three gas levels were within the normal ranges, indicating minimal risks.

Multiple linear regression analysis indicate that water level within the hand-hole, internal temperature, wire temperature, temperature of the cap, road width and distance from road edge were not statistically significant regressors for the oxygen level, with the regresstion coefficient (r2) of 0.1.

It is suggested to work outside the hand-hole. However, if entry is necessary, strict safety procedures for confined space should be followed, with an extra caution on the effectiveness of management and record keeping from the contractor.