Understanding bather load requirements in a swimming pool environment is all too often overlooked when designing an aquatic facility. While design considerations for an aquatic facility are commonly related to architectural and engineering aspects, allowable bather loads can also have long term impacts to your facility operations.
Bather load requirements generally vary amongst state swimming pool facility codes. Traditional approaches have focused on the premise that more swimmers will commonly be gathered within shallow water areas, as compared to deeper water areas. As a result, these customary design requirements use water surface area as the primary factor when determining bather load. Allowable load factors will vary based upon the water depths, with shallow water areas (less than 5’-0”) and deep water areas (greater than 5’-0”) separated into different categories. Many standards use 15 square feet per bather for water areas less than 5’-0” and 25 square feet per bather for deep water areas. Additional considerations are also given to the inclusion of water activities such as diving boards and water slides, where dedicated water area for each of these activities is subtracted from the overall water surface area. For example, many codes require 300 square feet of water surface area for each diving board, which will be deducted from the overall deep water area when calculating bather loads. In addition to the bather load allowances for shallow and deep water areas, some state swimming pool codes will include additional bathers in the facility based upon the amount of deck area that is provided. The reasoning with this additional bather allowance is there will likely be people who spend a portion of their time not in the water. An allowance for additional bathers as a result of pool deck might be 1 bather for every 50 square feet of excess pool deck. Excess pool deck is typically defined as all deck areas that are beyond the minimum requirements, which is commonly established at 4’-0” to 5’-0” from the pool edge. Additionally, the Model Aquatic Health Code (MAHC) also stipulates that deck areas beyond twice the amount of water surface area is treated differently than deck equal to or less than the water surface area.
While the aforementioned approach has been widely accepted in the swimming pool industry for many decades, the MAHC has considered a more scientific methodology to bather load calculations. The MAHC utilizes a Theoretical Peak Occupancy (TPO) as a means approach when assigning the maximum number of allowable occupants or users at an aquatic facility. The significant difference in the MAHC approach is the TPO calculations are based around the type of water in lieu of the water depths. The following water areas definitions can be found within the MAHC:
- Flat Water means an aquatic venue in which the water line is static except for movement made by users usually as a horizontal use as in swimming. Diving spargers do not void the flat water definition.
- Agitated Water means an aquatic venue with mechanical means (aquatic features) to discharge, spray, or move the water's surface above and/or below the static water line of the aquatic venue so people are standing or playing vertically. Where there is no static water line, movement shall be considered above the deck plane.
- Hot Water means an aquatic venue with a water temperature over 90oF (32oC).
- Stadium Seating means an area of high-occupancy seating provided above the pool level for observation.
- Specific Use Area mean water areas that are dedicated for a very specific use such as waterslide landing pool areas and interactive water play areas.
For each of the aforementioned areas the TPO is calculated by dividing the water surface area in square feet by the density factor (D). Density factors for water areas range from 20 SF per bather for flat water, 15 SF for agitated water, 10 SF for hot water and interactive play areas. For non-water related spaces density factors area considered such as 50 SF per bather for pool deck and 6.6 SF per bather for stadium seating. The overall TPO is then determined by adding the calculations for each aquatic venue within the aquatic facility. The scientific theory behind using the TPO approach is that the number of users should be based upon the impact from various water spaces and the anticipated users within these spaces. In addition to bather load, design parameters such as natatorium air handling systems are impacted by the TPO.
Ultimately, the determination of bather loads or theoretical pool occupancy will impact not only how many patrons will be allowed to use an aquatic facility, but significant design considerations must be given to locker room and restroom hygiene fixtures. Quantifying toilets, urinals and other hygiene fixtures, excluding showers, shall be based upon the greater of current applicable jurisdictional codes, or the MAHC calculated maximum theoretical peak occupancy. Lastly, consideration should always be given to what meets code requirements and what actually seems and feels reasonable. Whether bather load determinations are based upon water areas as segregated by depth or type of water, one must consider the reality of the bather load numbers, and use practical and common sense when assigning final loads. While exceeding code allotments may not be possible and certainly not recommended, a reduction in the allowable bather loads may be considered. This reduction in allowable theoretical peak occupancy may provide not only a relief from excessive hygiene fixture requirements, but may result in a better user experience.