依據勞工安全衛生設施規則之定義，局限空間係指非供勞工在其內部從事經常性作業，勞工進出方法受限制，且無法以自然通風來維持充分、清淨空氣之空間，但其並未規定須達多少深度或多大空間才屬之；就環境條件而言，電力手孔與人孔同屬埋設於道路地面下，故均符合局限空間自然通風不易維持之特性，而兩者最大差別在於其埋設深度與內部大小。本研究針對開啟後之三類電力手孔（共322座），以直讀式四用氣體偵測器（氧氣、硫化氫、一氧化碳、可燃性氣體），對其內部空氣進行量測，以評估其分佈特性。結果發現，640、810及1650型手孔出現缺氧(氧氣含量<18％)的比例分別為8.3%、1.6%及3.6%，總平均為3.4%，如未做任何通風及防護措施便進入其內部作業，勞工有發生缺氧危險之虞。而其他3項氣體指標則無異常。本研究針對1650型手孔的環境參數，如孔內積水深度、孔內水溫、孔蓋溫度、孔內接頭溫度、道路寬度、離路緣線距離等對孔內氧氣濃度進行複線性迴歸分析，結果顯示迴歸模式之解釋力(r2)僅10%，且個別自變數之迴歸係數均未達到統計上之顯著性。手孔作業時，應盡量減少孔內作業之必要性，如人員必須進入手孔，本研究建議將電力手孔列為局限空間作業，執行各項防制作為，並特別注意承攬商執行現場管理之有效性及記錄保存。

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.