HONOLULU, HI — After the collapse of the World Trade Center towers Sept. 11, people in the vicinity faced a new threat: the sudden release of tons of dust and debris into the air. Early reports warned of asbestos risks, then stated that the levels in the air were much lower than anticipated.

Many people didn’t believe it.

In order to clear the confusion, the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) presented a forum at its 2002 Annual Meeting here in Honolulu, titled “Particles: How Bad Was Ground Zero?”

The opening question was, “What are the dust levels involved when a building collapses?” It was known that the collapsed twin towers released asbestos, volatile organic compounds (VOCs), and particulates into the air, suddenly and practically unexpectedly. People were still evacuating the area — “just people, with no dust masks or respirators,” commented the moderator.

Six days afterward, there was still a dust cloud. What were cleanup workers exposed to? What were people working and living in nearby buildings exposed to?

What can we learn from this that may be applied to other catastrophic events, including volcanic eruptions and fires?

In New York and at the Pentagon building, many HVACR companies were involved in the cleanup in the aftermath of the Sept. 11 terrorist attacks. At Ground Zero, Hudson Technologies' 40-foot tanker trucks were parked just a few feet away from the upright steel beam cross that stood as a symbol of prayer and remembrance.


The Environmental Protection Agency’s (EPA’s) website,www.epa.gov, offers a history of data levels, stated an engineer. Sites were monitored for asbestos, PCBs, and lead. The EPA and other federal, state, and local agencies collected extensive environmental monitoring data from the World Trade Center site and nearby areas in Manhattan, Brooklyn, and New Jersey.

The forum reported results from Wall Street, Battery Park, Park Row, and Albany Street. Unfortunately, some of the monitoring didn’t start until November, so immediate levels are not known.

Wall Street is one such site. Monitoring started there in mid-November, said the engineer presenting the information. Particulate matter measuring 10 microns (PM10) was taken in 24-hour averages; 30- to 35-microgram per cubic meter (mg/cu m) PM10 concentrations were found to be fairly constant.

According to the presenter, “150 would be problematic for more sensitive population segments,” such as the elderly and people whose immune response is impaired.

Then in May 2002, those 24-hour averages peaked up to 100 mg/cum. Some speculated that it could have been due to last-minute cleanup efforts, before the official closing of the site.

Also at Wall Street, 2.5 micron particles (PM2.5) were measured. Daily numbers were around 15 to 20, the presenter said; the sensitivity level for the susceptible population is around 65. Fluctuations and overall stability correspond to levels of PM10, noting that watering down processes probably helped keep levels fairly low.

At Battery Park, maximum hourly numbers for PM2.5 were 15 mg/cu m or less, the presenter stated, noting that the site was “Out of the direct plume.”

Park Row measured larger, 10-micron particles (PM10). “I’m guessing this site was on the downwind side” of the towers, said the presenter. Its data were measured from mid-September. Numbers were “up into concern region,” around 65 mg/cu m. Decay in the numbers were consistent with reductions in the source over time.

At Albany Street, PM2.5 measured peaks almost up to 40, but mainly clustering at 10 to 15 mg/cu m. They also peaked hourly after May 24, 2002.


There are several unknowns:

  • What are normal, everyday PM concentrations in Manhattan?

  • What were the concentrations immediately following the towers’ collapse?

  • Could lower numbers of small particles have been due to the amount of larger particles?

    An engineer noted that “In bulk sampling on September 16 and 17, PM1.2 was 1% to 2% of the mass.” The largest “particles” were 53 microns. “I’m talking huge particles,” he said: “metal shreds, etc.”

    Filter manufacturers attending the forum noted that building owners were by far the most responsive to the situation, taking swift action to filter out the incoming air, and clean and test air within their buildings.

    At the rescue site itself, however, rescuers and other emergency personnel, caught up in the moment and pushed by adrenaline, mostly did not wear appropriate respiratory protection. “Early pictures show them with protection — right at the Adam’s apple,” commented a presenter. There is some speculation that permanent disability from the rescue now exceeds lives lost due to the event.

    “We have to insist that despite the adrenaline of the rush to save lives, people are putting themselves at risk,” stated an engineer.

    Will the Standard 62 committee consider IAQ for catastrophic events in its scope? It hasn’t to this point, said a committee member, but it will probably be taken into consideration.

    Publication date: 07/22/2002