8-2 OPERATONAL CONSIDERATIONS。 Batteries generate a small amount of hydrogen and other gases while they are being charged or discharged。  Hydrogen build- up could lead to an explosion。 Provide ventilation to keep the hydrogen concentration below 25 percent of the LEL (LEL = 4 percent) to prevent an accumulation of an explosive mixture。

8-3 DESIGN CRITERIA。 Design the facilities using NAVFAC DM-28。4, General Maintenance Facilities。  Design the ventilation system using general technical requirements in chapter 4 of this UFC and the specific requirements in this Chapter。

8-3。1 Exhaust System。 Design exhaust ventilation to have both high-level exhaust for hydrogen and low-level exhaust for electrolyte spills (acid fumes and odors)。 Distribute one-third of the total exhaust flow rate to the high-level exhaust to ventilate all roof pockets。  Locate low-level exhaust at a maximum of 304。8-mm (1-ft) above the floor。  See Figure 8-1 for a floor plan of a battery maintenance room。

8-3。1。1 Minimum Flow Rate Calculation。  To determine the amount of required volumetric airflow rate, the amount of hydrogen produced must be calculated for the total number of battery cells in the room。 The volume of hydrogen generated is governed by the amount of charging current (ampere) supplied to the fully charged battery by the charger。 Significant amounts of hydrogen are evolved only as the battery approaches full charge。 To determine a minimum required volumetric airflow rate, use the following formulas:

C = (FC/100) x AH x K x N (1)

Q = (C/60)/ PC (2)

Figure 8-1。  Ventilation system for battery maintenance facilities。

Where:

C = Hydrogen generated, in cubic feet per hour (cfh)。

FC = Float current per 100 ampere-hour。  FC varies with battery types, battery condition, and electrolyte temperature。 It will double/halve for each 15 degrees F (8 degrees C) rise/fall in electrolyte temperature。

AH = Ampere hour。

K = A constant of 0。016 cubic feet of hydrogen per 1 ampere-hour per cell (at sea level and 77 degrees F ambient temperature)。

N = Number of battery cells。

Q = Minimum required ventilation airflow rate, in cubic feet per minute (cfm)。

PC = Percent concentration of hydrogen allowed in room (PC = 0。01 to keep the hydrogen concentration at 1 percent)。

Formula (2) assumes complete mixing of the air inside the battery maintenance facility。  In most cases, use a safety factor k to determine the actual ventilation rate。

See Figure 2。1 of the ACGIH IV Manual to select a “k” value。

QA = Q x k (3)

QA = The actual volumetric ventilation rate, in cubic feet per minute (cfm), which can be expressed in air change per hour (ACH) using the following formula: