VENTILATION 1 CAR PARKS
Left: Testing of a car park’s ventilation. Right: The Manchester Transport Interchange Development uses offset glass panels to obscure the sight of the cars, while maintaining adequate free area so that it benefits from natural ventilation as well as being protected from the weather
hour) and then, in the case of a fire, ramped up to provide 10 air changes per hour. However even at three air changes per hour the air movement through the extract system is significant, since each equivalent car parking space will require a minimum air movement of approximately 120 cu m/ hour. By employing variable speed fans,
controlled using carbon monoxide sensors, the flow rates can be automatically reduced to practically zero at times when there are no vehicle movements in the car park (at night and, for office car parks, mid mornings and afternoons as well as at weekends). This will additionally ease the requirement for noise attenuation of the extract system as, during non-working periods and particularly at night, the extract fans will be running at lower speeds. The overriding design requirement for
Air quality Impact of carbon monoxide
The principal measure of air quality in car parks is the level of carbon monoxide (CO) level in parts per million. (1ppm = 1.145 mg/cu m and 1mg/cu m = 0.873 ppm). The background levels in remote country areas and across the sea are likely to be less than 0.5ppm (parts per million). Non-smoking healthy humans will breathe out less than 3ppm, and those less healthy or stressed in some way up to around 15ppm. Smokers may exhale up to 30ppm. Exposure to CO affects the ability
in healthy humans to exercise, and those who are elderly or predisposed to angina, or asthma can be particularly affected. The World Health Organisation- recommended levels are based on the carbon monoxide exposures to maintain the effect on blood
56 CIBSE Journal May 2011
carboxyhemoglobin (COHb) for a resting adult at levels deemed safe (currently 2%). And the resulting guidelines are set in terms of short- term peak exposures that might occur, for example, while queuing in traffic in a car park; and for longer periods of one hour (that may be relevant for transitory parking attendants) and for eight hours that is used for general occupational exposures (working full-time in the car park).
EXPOSURE PERIOD>> WHO*
US EPA* UK Building Regs England/Wales Building Regs Part F – car parks
90ppm 90ppm
60ppm The US Environmental
Protection Agency is currently reviewing its carbon monoxide standards, but looking to maintain the levels at those shown in the table that were set in 1971. However, this is highly contentious as many cited studies indicate that CO levels with marginal increases above the background (and less than 5ppm) can have significant effects on health, with increased risks of ill health, including respiratory
15 MINUTES 87ppm
30 MINUTES
and cardiovascular disease, from relatively small CO increases and not necessarily correlated with high COHb levels. There is pressure on the EPA to set the new eight-hour standard to no more than 1ppm, and the one-hour standard to no more than 5ppm. This would be a major change in the required levels, and may significantly influence the operation of car park ventilation with inevitable influence on global design.
1 HOUR 30ppm 35ppm 30ppm
8 HOURS 9ppm 9ppm
10ppm 30ppm
Comparative standards for limiting carbon monoxide levels (*World Health Organisation **Environmental Protection Agency)
www.cibsejournal.com
car park ventilation is that of providing the safest environment in the event of a fire. But in meeting this essential need the remainder of the operational period (in fact practically 100% of the time) must not be neglected as this will not only affect the health of operatives and users, but potentially significantly impact on operational cost and resulting carbon emissions. Through using design tools such as
computational fluid dynamics, and a system incorporating distributed sensors and intelligent controls, the application of impulse ventilation in conjunction with appropriate supply and extract systems can provide opportunities to meet the whole-life needs of car park ventilation.
l With thanks to Ross BaRRitt at Flakt Woods for technical information and images
Flakt Woods
Ian Simpson Architects
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