System Design
06-237619-001 3-9 April 2020
3-8 DESIGN FACTORS
The basic quantity of Agent required may be further modified to suit any special conditions that
would adversely affect the usual extinguishing efficiency. Such conditions could include
unclosable openings, reigniting from heated surfaces, enclosure geometry, and obstructions
which impinge on the distribution pattern of the nozzles.
The design quantity shall further be adjusted to compensate for changes in the ambient
pressure of more than 11% from the standard sea level value (see Section 3-8.8).
In each case, it is the project engineer’s responsibility that the design concentration is chosen
under the following conditions:
• Integrity of the room, unclosable openings, unstoppable extraction ventilating, etc
• Combustible flammable materials involved
• Quantity of flammable material that may be expected within the enclosure
• Design concentration exceeding that required by most demanding flammable materials
• Ventilation conditions (re-circulating air handling units, stoppage of ventilation, etc)
• Altitude of the protected risk (Atmospheric Correction Factor)
• Escape routes and time required to vacate the risk
• Personnel safety in general
3-8.1 Electrical Clearance
When exposed electrical conductors are present in the protected enclosure, the clearance
between those conductors and all parts of the system that may be approached during
maintenance shall not be less than those listed below. Where these clearances cannot be
achieved, warning notices shall be provided and a safe system of maintenance work shall be
adopted.
Table 3-6. Electrical Clearance
Rated
Voltage
Minimum clearance from any point on or about the permanent equipment
where a person may be required to stand (measured from foot position)
kV
To the nearest unscreened live
conductor in air (section
clearance)
To the nearest part of an insulator not at
earth potential which supports a live
conductor (ground clearance)
15 8.53’ (2.60 m) 8.20’ (2.50 m)
33 9.02’ (2.75 m)
44 9.51’ (2.90 m)
66 10.17’ (3.10 m)
88 10.50’ (3.20 m)
110 10.99’ (3.35 m)
132 11.48’ (3.50 m)
165 12.47’ (3.80 m)
220 14.11’ (4.30 m)
275 15.09’ (4.60 m)
“Insulator” includes all forms of insulating supports, such as pedestals and suspension insulators,
bushes, cable sealing ends and the insulating supports of certain types of circuit breaker
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