{
  "note": "Every quotation on the page, with the passage it comes from. Each excerpt is copied from the kept copy named in 'kept' (whitespace collapsed); for the scanned NBS reports and Cosgrove the kept copy holds a transcription read from the page image, because the OCR garbles fractions, hyphens and columns. Fetched 2026-11-01.",
  "quotes": {
    "bms-purpose": {
      "source": "French and Eaton, Self-Siphonage of Fixture Traps, NBS BMS126 (1951), Foreword signed E. U. Condon, Director, p. III",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "The purpose of the trap is to interpose between the sewer and the interior of the building a water seal that will prevent sewer air from passing back into the building and causing offensive odors there. This water seal is normally from 2 to 4 inches in depth and is sufficient to prevent the passage of sewer air into the building under any ordinary conditions. However, if, through self-siphonage or any other cause, part of the water seal in the trap is lost, then the pressure fluctuations in the drainage system of the building, which occur as the result of the discharge of the fixtures on the system, may be great enough to bubble sewer air back through the trap seal."
    },
    "bms-dip": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 7",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "When it has reached the value unity, this means that the water has been removed from both legs of the trap down to the dip of the trap and that minute changes of pressure in the proper direction will suffice to force sewer gas into the building."
    },
    "m31-trapseal": {
      "source": "Wyly and Eaton, Capacities of Stacks in Sanitary Drainage Systems for Buildings, NBS Monograph 31 (1961), p. 2, a definition the monograph takes from the American Standard National Plumbing Code A40.8-1955",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-monograph-31-1961-excerpts.txt",
      "excerpt": "The trap seal is the maximum vertical depth of liquid that a trap will retain, measured between the crown weir and the top of the dip of the trap."
    },
    "bms-defies": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 11",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "has made it clear that we are concerned with an extremely complicated problem, one which defies analytical treatment."
    },
    "bh13-half": {
      "source": "R. B. Hunter and L. W. Snyder, Physics of plumbing systems, ch. 6 of Recommended Minimum Requirements for Plumbing (Bureau of Standards, revised August 30, 1928), p. 137",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "An S or a P trap seal may be drawn to the point of breaking the seal with a loss of approximately one-half its full seal, after which it may be subjected repeatedly to the same or a smaller strain with no further loss of seal."
    },
    "bms-weir": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 7",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "The water thus displaced flows over the trap weir and down the drain, and thus is not available to refill the trap when the pressures on the two sides of the trap seal equalize."
    },
    "bms-one-investigator": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 7",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "One investigator [4, p. 137] has proposed that a value of 1/2 be used as the value of h/t to constitute the dividing line between satisfactory and unsatisfactory performance of the trap."
    },
    "bms-twice": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 31",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "The latter method would require an investigation of the probability of a positive pressure equal in magnitude to twice the remaining trap seal occurring at the same time as the remaining trap seal in question."
    },
    "bms-pumping": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 7",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "The critical trap-seal loss is the maximum loss that can occur in the trap, unless the pressure reduction in the drain becomes and remains for an appreciable length of time so excessive that air is sucked from the inlet leg of the trap through the water seal into the drain, and in this process carries with it some of the water in the trap by what may be called a pumping process."
    },
    "bms-equal-radii": {
      "source": "French and Eaton, NBS BMS126 (1951), p. 7",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BMS/nbsbuildingmaterialsstructures126.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bms126-1951-excerpts.txt",
      "excerpt": "By making the assumption that these two radii are equal, a considerable simplification in the computations results, as will appear in the analysis to be given."
    },
    "m31-drags": {
      "source": "Wyly and Eaton, NBS Monograph 31 (1961), p. 19",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-monograph-31-1961-excerpts.txt",
      "excerpt": "The principal cause of air movement in building drainage systems is the friction developed between the high-velocity layer of water flowing down the drainage stack and the core of air which it encloses. The friction thus developed drags air along with the water."
    },
    "bh13-pressures": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 110",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "In all cases back pressures only were encountered at the base of the stack. The region of back pressures extended upward as the volume of the discharge was increased. In the upper portions of the stack below the entrance point of the discharge partial vacuums only were encountered. Between these two is a region in which the pressure alternates between positive and negative pressures measured from atmospheric pressure as the zero."
    },
    "m31-least": {
      "source": "Wyly and Eaton, NBS Monograph 31 (1961), p. 39",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-monograph-31-1961-excerpts.txt",
      "excerpt": "Least pressures occur immediately below a point of water entrance, and greatest pressures occur near the base of the stack. The pressure at any point is a function of rate of discharge, elevation of point of water entrance, degree of venting, and geometry of the system."
    },
    "bh13-unvented": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 110",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "Figures 42 and 43 illustrate the pressure effects in a 3-inch stack, unvented except by the open stack top. [...] These pressures, especially the partial vacuums, are not necessarily those in the center of the stack, but rather the pressures that would be produced in an unvented branch line connecting at that point."
    },
    "bh13-above": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 155",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "Pressure measurements made in the complete plumbing test installations and in straight 3-inch stacks at points on the stack above the inlet through which water was introduced into the stack showed no measurable effects when the stack top was open. At the same level as the inflow only very slight suctions or back pressures were produced."
    },
    "bh13-31in": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 114",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "PRESSURE EFFECTS IN A STACK-VENTED SYSTEM.-With the 3-inch stack 33 feet long (fig. 46) unvented except through the open top water was introduced through a P trap and Y fitting at the rate of 200 gallons per minute and measurements taken in 3-inch Y fittings at intervals of 5 feet 10 inches, beginning at a point 10 inches below the entrance point. The mean of two independent sets of measurements is plotted in Figure 47. The maximum of any individual pressure reading was 31.3 inches of water vacuum at the point 10 inches below the entrance point."
    },
    "bh13-pm1": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 114",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "(3) that no positive or back pressure greater than 1 inch and no negative pressure or partial vacuum less than 1 inch of water, measured from atmospheric pressure as the zero, is to be developed in any branch drain connecting to the stack above the house drain."
    },
    "m31-negligible": {
      "source": "Wyly and Eaton, NBS Monograph 31 (1961), p. 20",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph31.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-monograph-31-1961-excerpts.txt",
      "excerpt": "If this range of pressure can be maintained, the effects of pneumatic-pressure fluctuations on the fixture-trap seals will be negligible."
    },
    "adh-25": {
      "source": "Approved Document H (2015 edition), para 1.3",
      "url": "https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/uk-approved-document-h-2015-excerpts.txt",
      "excerpt": "Under working and test conditions traps should retain a minimum seal of 25mm of water or equivalent."
    },
    "bh13-terms": {
      "source": "Hunter and Snyder, in Recommended Minimum Requirements for Plumbing (1928), p. 171",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "\"Blown\" means water thrown up from the closet bowl or out of the bowl by back pressure. \"Bubble\" or \"bubbles\" means a small quantity of air forced back through the trap by back pressure."
    },
    "bh13-safety": {
      "source": "Subcommittee on Plumbing, Recommended Minimum Requirements for Plumbing (1928), p. 54",
      "url": "https://nvlpubs.nist.gov/nistpubs/Legacy/BH/nbsbuildinghousing13.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/nbs-bh13-1928-excerpts.txt",
      "excerpt": "While it is true that a seal is not actually broken unless the water in the trap falls below the \"dip,\" some factor of safety must be allowed to provide for unexpected shocks, for evaporation, capillary loss, and for oscillations due to wind pressure, while a lowering of the seal exposes a foul surface on the house side of the trap."
    },
    "cosgrove": {
      "source": "J. J. Cosgrove, Principles and Practice of Plumbing (1906), p. 45",
      "url": "https://archive.org/details/principlespracti00cosguoft",
      "kept": "research/the-water-between-you-and-the-sewer/sources/cosgrove-1906-excerpts.txt",
      "excerpt": "it can be calculated that under ordinary conditions the seal of an unvented siphon trap with a 1 3/4-inch depth of seal will be destroyed in from four and a half to five weeks' time. It may be stated, as a general rule applicable to all types of unvented traps, that under ordinary conditions such as obtain in a well constructed drainage system, the rate of evaporation will average .4 of an inch per week, irrespective of size or shape of the surface exposed. No experimental data is available to show the rate of evaporation of water from ventilated traps, but it would be safe to assume a rate of .8 of an inch per week."
    },
    "adv24": {
      "source": "Buildings Department, Hong Kong, Practice Note ADV-24, Floor Drains in Kitchens and Bathrooms (first issue June 2003; the text quoted is the re-issue of August 2009)",
      "url": "https://www.bd.gov.hk/doc/en/resources/codes-and-references/practice-notes-and-circular-letters/pnap/ADV/ADV024.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-bd-adv24-floor-drains-2003.txt",
      "excerpt": "The water in the trap may dry up through evaporation unless water is replenished, from time to time, by the occupants or through discharge of waste water."
    },
    "doh-stacks": {
      "source": "Department of Health, Hong Kong, Outbreak of SARS at Amoy Gardens: Main Findings of the Investigation (17 April 2003), para 7",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "Each block has eight vertical soil stacks each collecting effluent from the same unit of all floors. The soil stack is connected with the water closets, the basins, the bathtubs and the bathroom floor drains."
    },
    "doh-filled": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 7",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "For this preventive mechanism to function properly, the water traps must be sufficiently filled with water."
    },
    "doh-321": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 3",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "As of 15 April 2003, there were a total of 321 SARS cases in Amoy Gardens. There was an obvious concentration of cases in Block E, accounting for 41% of the cumulative total."
    },
    "expcom-329": {
      "source": "SARS Expert Committee, SARS in Hong Kong: from Experience to Action, ch. 3, para 3.67",
      "url": "https://www.sars-expertcom.gov.hk/english/reports/reports/files/e_chp3_23.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/sars-expert-committee-ch3-community-outbreak.txt",
      "excerpt": "At the end of the outbreak, a total of 329 residents had been infected, with 42 deaths."
    },
    "doh-mopping": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 8",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "However, as most households had the habit of cleaning the bathroom floor by mopping instead of flushing it with water, the U-traps connected to most floor drains were likely to be dry and would not have been functioning properly. Indeed, in tests carried out in one of the units in Block E, reflux of air from the soil stack into the bathroom through the floor drain was demonstrated when the exhaust fan in the bathroom was switched on. It is postulated that the reflux could have contained droplets of contaminated sewage present in the soil stack, be dispersed into the bathroom, and be extracted by the bathroom exhaust fan into the light well between adjacent units."
    },
    "doh-heading": {
      "source": "Department of Health, Hong Kong (17 April 2003), heading before para 12",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "PROBABLE EXPLANATION OF THE OUTBREAK"
    },
    "doh-pathway": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 15",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "The bathroom floor drains with dried-up U-traps provided a pathway through which residents came into contact with small droplets containing viruses from the contaminated sewage. These droplets entered the bathroom floor drain through negative pressure generated by exhaust fans when the bathroom was being used with the door closed."
    },
    "doh-probable14": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 14",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "It is probable that the index patient initially infected a relatively small group of residents within Block E and subsequently to the rest of the residents in that block through the sewage system, person-to-person contact and the use of shared communal facilities such as lifts and staircases."
    },
    "who-dry": {
      "source": "WHO Environmental Health Team, report on Amoy Gardens (released 16 May 2003), Conclusions",
      "url": "https://www.info.gov.hk/info/sars/who-amoye.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/who-environmental-health-team-amoy-2003-05-16.txt",
      "excerpt": "At the time of the outbreak, the floor drain traps in many apartments seemed to have not been filled with water for long periods. Thus they had lost their sealing function and generated an open connection to the soil stack. In the case of a running exhaust fan and a closed door, droplets would have been drawn from the soil stack into the bathroom through the floor drain. This could have contaminated the bathroom."
    },
    "who-concluding": {
      "source": "WHO Environmental Health Team (released 16 May 2003), Concluding remark",
      "url": "https://www.info.gov.hk/info/sars/who-amoye.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/who-environmental-health-team-amoy-2003-05-16.txt",
      "excerpt": "It seems highly likely that an unfortunate sequence of environmental and health events happened simultaneously and contributed to the spread of the SARS-related coronavirus in the Hong Kong residential estate of Amoy Gardens."
    },
    "press-combination": {
      "source": "Hong Kong Government press release, WHO investigation findings support HK's work (16 May 2003), Health Bureau website",
      "url": "https://www.healthbureau.gov.hk/en/press_and_publications/press/2003/press030516a.htm",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-press-2003-05-16-who-team.txt",
      "excerpt": "Dr Leung noted that both the findings of the WHO and the Department of Health indicated that the outbreak at Amoy Gardens was highly likely to be caused by a combination of events."
    },
    "doh-airborne": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 16",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "Transmission of the disease by airborne, waterborne route and infected dust aerosols have been examined but these were not supported by the epidemiological picture and laboratory results."
    },
    "doh-windows": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 8; the sentence runs across a page break and begins \"The contaminated\" at the foot of page 2, after \"It is postulated that the reflux could have contained droplets of contaminated sewage present in the soil stack, be dispersed into the bathroom, and be extracted by the bathroom exhaust fan into the light well between adjacent units.\"",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "droplets could then enter other units through open windows."
    },
    "yu-airborne": {
      "source": "Yu IT et al., Evidence of airborne transmission of the severe acute respiratory syndrome virus, N Engl J Med 2004;350(17):1731-9, abstract",
      "url": "https://doi.org/10.1056/NEJMoa032867",
      "kept": "research/the-water-between-you-and-the-sewer/sources/pubmed-yu-2004-nejm-airborne-amoy.txt",
      "excerpt": "Airborne spread of the virus appears to explain this large community outbreak of SARS, and future efforts at prevention and control must take into consideration the potential for airborne spread of this virus."
    },
    "yu-plume": {
      "source": "Yu IT et al., N Engl J Med 2004, abstract",
      "url": "https://doi.org/10.1056/NEJMoa032867",
      "kept": "research/the-water-between-you-and-the-sewer/sources/pubmed-yu-2004-nejm-airborne-amoy.txt",
      "excerpt": "examined the correlation of these data with the three-dimensional spread of a virus-laden aerosol plume that was modeled using studies of airflow dynamics."
    },
    "doh-ventpipe": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 9",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "The cracked sewer vent pipe could have emitted droplets carrying contaminated sewage into the light well every time a toilet was flushed."
    },
    "who-ventpipe": {
      "source": "WHO Environmental Health Team (released 16 May 2003), Results",
      "url": "https://www.info.gov.hk/info/sars/who-amoye.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/who-environmental-health-team-amoy-2003-05-16.txt",
      "excerpt": "There is no strong enough evidence to link the broken vent pipe discovered at the bottom of the light well to the spread of the virus."
    },
    "kang-limit": {
      "source": "Kang M et al., Probable Evidence of Fecal Aerosol Transmission of SARS-CoV-2 in a High-Rise Building, Ann Intern Med 2020;173(12):974-980, abstract",
      "url": "https://doi.org/10.7326/M20-0928",
      "kept": "research/the-water-between-you-and-the-sewer/sources/pubmed-kang-2020-guangzhou-high-rise.txt",
      "excerpt": "LIMITATION: Inability to determine whether the water seals were dried out in the flats of the infected families."
    },
    "doh-advice": {
      "source": "Department of Health, Hong Kong (17 April 2003), para 19",
      "url": "https://www.info.gov.hk/info/sars/pdf/amoy_e.pdf",
      "kept": "research/the-water-between-you-and-the-sewer/sources/hk-doh-amoy-main-findings-2003-04-17.txt",
      "excerpt": "Residents of Amoy Gardens were advised to ensure the water level at the U-traps of drainage outlets to ensure proper functioning."
    }
  }
}