The door that separates sewing department A from sewing department B in director Pham's factory, Bình Tân district, Ho Chi Minh City, is a double-leaf door of light grey metal with the placard P-12B. It was installed, Hà Thị Linh told me later in the courtyard during the lunch break, in March of two thousand and nineteen, by the maintenance worker Quân, now seventy-three, who calibrated its return spring to three and a half seconds on the back of a shoe delivery slip.

Department A has had air conditioning since March. Department B has six ceiling fans. The difference, at nine in the morning, is seven degrees. The difference, at fourteen hundred, is nine degrees. The difference, Linh told me, is the reason why last week Một, fifty-two, row five, fainted between row three and row four and fell on the cement floor. Pham did not file a report. Hương brought her back to the machine after twelve minutes.

Linh is thirty-one, has been at the factory for four years, row four machine seven. Every month she sends two million four hundred thousand dong to her family. One million nine hundred thousand for her brother's tuition, twenty-one, second-year electrical engineering at the University of Cần Thơ. Five hundred thousand to her mother, sixty-eight, in Bến Tre, for blood pressure medicine.

This morning at five forty-six, before the start of the shift, director Pham stopped maintenance worker Quân in the courtyard and told him that tomorrow, Saturday, he had to come check the spring of door P-12B because the wear, Pham said, was anomalous. Quân said yes. Pham left. Quân, Linh told me, looked toward department B for a moment and then kept walking toward the workshop.

At six fourteen, during the first bobbin change of the day, Linh opens door P-12B. She opens it all the way. The flow of cold air from department A enters department B with a low sound. Then, hearing Hương's steps in the central corridor, Linh returns the door to an opening of about thirty centimetres and rests it with her right foot on the metal threshold. The sandal, black rubber size thirty-six, sole worn under the big toe, rests half inside the threshold and half outside.

From that moment on, every twenty-two minutes or so, Hương walks through the corridor. The door stays at thirty centimetres. Linh's foot does not move.

Bích Trâm, twenty-three, row four machine eight, moves her Juki forty centimetres toward the door. Một, the one who had fallen last week, moves hers thirty. Hà, thirty-seven, row two, brings a towel from the coffee break and lays it on the floor where the oil from the machine nearest the door drips, because oil on cold air turns slippery and today, Linh told me, no one must fall.

At nine twenty-four, the analogue thermometer reads thirty-two degrees in the half of the department near door P-12B. Thirty-seven degrees in the far half. The difference, Linh told me, is five degrees, and five degrees is the difference between a shirt sewn well and a shirt sewn as best one can.

At ten eleven, the Juki on row three machine two breaks down. The pinion of the presser foot jumps two teeth. The worker at that station, Diệu, twenty-eight, walks through door P-12B to ask supervisor Khánh in department A for a replacement presser foot. There is no presser foot in A. Khánh calls maintenance worker Quân by radio. Quân answers from the workshop and says to wait eight minutes.

For the next forty minutes door P-12B stays completely open. Linh does not move her foot. Quân crosses twice, on the way out toward the storeroom of department B to fetch the pinion, on the way back toward department A with the presser foot. The second time, leaving, he rests his right hand on the stainless steel handle for a moment. The handle, Linh told me later in the courtyard, at ten fifty-one is cold. The flow of air from department A has hit it for forty minutes.

At ten fifty-one, Diệu starts the Juki up again. The door goes back to thirty centimetres. Linh's foot goes back onto the threshold.

Hương had not been through department B since nine forty-six. At eleven thirty-eight, Hương stops in front of door P-12B. Linh is sewing the hem of a white short-sleeved shirt, size M, batch 04-26-3. The machine hums. The thermometer behind machine seven reads thirty-three point two. Linh's shirt is wet under her arms and along her spine. Her right foot has been on the metal threshold for five hours and twenty-four minutes. The sandal has left a half-circle of damp on the rubber gasket of the door.

Linh does not move her foot.

Three seconds. Hương looks at the foot. Hương looks at Linh. Linh does not meet her gaze, she sews. Hương says one single thing, in a low voice, and says «two thousand and thirteen, twenty-two». Then Hương turns and resumes her round.

Linh knows what it means. Twenty-two was the number of workers in department B in two thousand and thirteen, when Hương herself entered the factory as a worker, row three, machine ten. Twenty-two, Linh told me later in the courtyard, is the number of women who had to sign the renunciation of the three additional summer breaks in order to obtain the ceiling fans, the six fans that today turn above Linh's head and are not enough. Hương signed first.

At twelve oh three, director Pham comes in from the central corridor with the radio in his hand. The radio is broadcasting on speaker a male voice in American English, southern accent, that says a figure and then says «final order, no further movement», and then a pause, and then «we'll see in two weeks». Pham stops in front of door P-12B. Pham looks at the open door. Pham looks at Linh's foot. Pham looks at Linh. Linh sews. Pham does not call Hương. Pham lowers the radio and turns toward department A. The American voice says something else. Pham leaves.

The door stays open.

Eighteen hundred. The end-of-shift siren sounds. Linh moves her foot. The door closes in three and a half seconds, the way Quân had calibrated it in March of two thousand and nineteen. Linh bends over the metal threshold to refasten the buckle of her right sandal, which the pressure of the shift has loosened. The buckle gives a small brass click. Linh straightens up.

Linh leaves with the other workers of department B toward the courtyard. The cold air, Linh told me, stays in department B for about ten minutes after the door closes. Then no more. Tomorrow maintenance worker Quân, who is seventy-three and has a tiny handwriting on the back of shoe delivery slips, comes to check the spring. Linh doesn't know, she told me, whether Quân will write a second calculation on the back of the slip, or whether he will fold the slip back into the file without adding anything. Quân has been Hương's friend since two thousand and nineteen. Quân has been Pham's employee since two thousand and ten.

Linh rides home on her motorbike. Her room is in alley forty-eight of Bình Long street, twenty-two minutes from the factory. At four in the morning, a motorbike enters the alley and stops two doors further on. It is the neighbour, Châu, coming back from the night shift at the Pou Yuen shoe factory. Châu kills the engine. Linh hears the key turn in the lock.