(6) Ventilation intakes of enclosed machinery spaces contiguous to hazardous areas and contain- ing internal combustion engines and boilers; and

(7) Ventilation intakes and near other openings of accommodation spaces.

2. At least two portable gas monitoring devices should be provided, each capable of accurately meas- uring a concentration of flammable gas.

3. The gas detectors are to be connected to an audible and visible alarm system with indicators on the drill floor and at the required emergency control stations. The alarm system is to clearly in- dicate the location and concentration of the gas hazard. The combustible gas detectors are to alarm at not more than 25 % and at 60 % of the lower explosive limit.

309. Hydrogen sulphide detection and alarm system

1. A fixed automatic hydrogen sulphide gas detection and alarm system is to be provided to the sat- isfaction of the Society so arranged as to monitor continuously the drilling area, mud processing area and well fluid test area of the unit and capable of giving audible and visual alarm at the main control points. The system is clearly to indicate where gas has been detected.