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It's mind-numbing. There has been a sense of helplessness in the city – thousands of people have been lining the streets to volunteer to help.

We have been organising teams to go down to sites to assist with search and rescue operation. It is some comfort to be a structural engineer as we are able to help. People have been working eight to 12 hour shifts. We've been called upon to give instant advice – is it safe to go in there? Can we move that? There are no calculations we can make to guide us, which is a little scary.

I was there from 4pm Saturday to 2am Sunday morning. It's like daylight down there, with all the lights. It's a situation you don't want to think about too much. It's emotionally draining. Contractors pull away steel: if there are any openings we go in with federal emergency agents and walk on the debris to check out the state of the voids. If we think it's stable we let the search and rescue teams in with the dogs. It's very slow going – as soon as something is found, everything stops as an examination of the area is carried out.

When you are there you are standing on 20 ft of rubble – you are standing on what used to be a tower. The 20 ft of rubble used to be a 100-storey building. It's just incredible. It's very difficult to comprehend what's gone on. Your mind blocks it off; it cannot accept it. There will be a long slog of work to do – just trucking out the material will take months. A big problem has been the fires. You pull a piece of debris and they flare up as they are fed oxygen. We'll be on call for some time. There are still precarious elements in the surrounding buildings. One nearby building has a piece of the tower's two-metre perimeter frame embedded in it.

Because of an event like this there is a sense of coming together and camaraderie – that's just fantastic. The city has been overwhelmed with help – bottled water, protective clothing, volunteer workers. One of our engineers finished his shift on Sunday morning. I gave him $20 for a cab. As soon as he got in the driver said: "Wherever you want – it's on me." This was a New York cab driver – they're not renowned for their generosity.

Our office was closed from Wednesday on. Grief counsellors are on offer to our staff – many of them witnessed the collapse from our windows. There are a lot of very traumatised people here. The mayor, Rudolf Giuliani, is saying the best way for the city to go forward is to get back to work. But it's still very quiet. I came to the office on the train, but there were only a few people on it. When I got to Grand Central Station, it was like a ghost town.

It's been harrowing. We've seen some gruesome things. But there is a strengthening of resolve, not a weakening. There were reports of people being pulled out of buildings in Turkey 12 days after its earthquake in 1999, so you never know.