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Ordinance on Safety and Health of Work under High Pressure
(Revised in terms of the Title March 19, 1977 by Ministry of Labour Ordinance No. 2)
Ministry of Labour Ordinance No. 40, September 30, 1972

Latest Amendments:
Ministry of Health, Labour and Welfare Ordinance No. 171 of July 16, 2001
In Japanese

Chapter III.  Management of Work

Section 2.  Management of Work in Compressed Air

(Prohibition of Entrance into Work Areas)

Article 13.The employer shall prohibit those other than persons directly concerned from entering the man-lock and work chamber, and shall put up a notice which can easily be identified outside the caissons, diving bells, compressed shields, etc., stating the prohibition.

(Rate of Compression)

Article 14.When the employer applies compression to the compressed air workers in a man-lock, the employer shall increase the pressure at a rate not higher than 0.08 MPa/min.

(Time Spent under High Pressure)

Article 15.When the employer has workers engage in work in compressed air, (restricted only to those types carried out under barometric pressures of 0.1 MPa or more, same as in this Article), the employer shall not make the compressed air workers engage in the said work in compressed air in violation of the standards on time given below for which the said workers are allowed to engage in the said work.

  1. The time, starting off from commencing the compression on the compressed air workers till commencing the decompression on them, (hereinafter called the "time spent under high pressure") shall be limited as set forth in the following (a) or (b).
    1. In case the numbers of shifts of work in which the employer has the compressed air workers engage in the said work in compressed air does not exceed twice per day and in addition the pressure imposed on the said workers does not exceed 0.4 MPa, the times given below are allowable:
      1. In terms of the first shift of work in compressed air (inclusive of the case in which the work in compressed air is carried out once per day); the longest time of those listed in the "Time under high pressure" column of Attached Table 1 depending upon the division of the "Pressure" column of the said Table, on the basis of the pressures used for the said work in compressed air.
      2. In terms of the second shift of work in compressed air; the time as listed in the "Time under high pressure for the second shift" column of Attached Table 1 depending upon the direction of the "Pressure" column of the said Table and the "Time under high pressure" column of the said Table in accordance with the time under high pressure used for the first shift, on the basis of the pressure used for the said work in compressed air (which corresponds to the one used for the first shift, if the pressure used for the first shift is higher than that for the second shift).
    2. In case the number of shifts of work in compressed air conducted by compressed air worker exceeds two per day or the pressure used for the work in compressed air exceeds 0.4 MPa , the times allowable are given below:
      1. In the terms of the first shift of work in compressed air (inclusive of the case in which the work in compressed air is carried out once per day); the longest time of those listed in the "Time under high pressure" column depending the classification of the "Pressure" column of Attached Table 2 on the basis of the pressures used for the said work in compressed air. 
      2. In terms of the second or following shift of work in compressed air; the time which is subtracted from the time which is obtained from Attached Table 3 (hereinafter called "corrected time for compressed air workers") from the longest time of those listed in the "Time under high pressure" column of Attached Table 2 depending upon the division of the "Pressure" column of the said Table on the basis of the pressure used for the said shift of work in compressed air (maximum pressure, in the case in which the pressure used for the work in compressed air already done by the said workers in the day is higher than that used for the said work in compressed air) (when a total of time, during work in compressed air is longer than the time set forth in the "Time under high pressure per day" column in accordance with the classification of the pressures as listed in the "Pressure" column of Attached Table 2 on the basis of the maximum pressure used for work in compressed air, and imposed on the said workers, the time is available by further subtraction of the differences between the said total of the time and those set forth in the "Time under high pressure" column from the said longest of time of those described in the "Time under high pressure" column). 
  2. When the employer has compressed air workers who have already engaged in work in compressed air further engage in the said work within a day, the employer shall provide the compressed air workers with a time, upon the completion of last decreasing gas pressures, which is longer than those set forth in the following (a) or (b), as the time for which to make decrease in the gas coefficients in the body of the compressed air workers (hereinafter called "time for decompression for the compressed air workers), and shall not make the compressed air workers further engage in heavy work for the said time.
    1. When there occurs a case which corresponds to that set forth in (a) of the preceding item; the time as listed in the "Time for decreasing gas pressure between shifts of work in compressed air" column of Attached Table 1 in accordance with the classification set forth in the "Pressure" column and also in the "Time under high pressure" column of the said Table on the basis of the pressure and the time under high pressure used for the first shift of work in compressed air.
    2. When there occurs a case as set forth in (b) of the preceding item; the time as listed in the "Time for decreasing gas pressure between shifts of work in compressed air" column of Attached Table 2 in accordance with the classification set forth in the "Pressures" column and also in the "Time under high pressure", column of the said Table on the basis of the pressure and the time under high pressure used for the final shift of work in compressed air.
  3. When the employer shall provide compressed air workers who have completed the work in compressed air for that day with the time, upon the completion of last decompression, which are longer than those set forth in the following a or b, as the time for decreasing gas pressures for the compressed air workers, and shall not make the compressed air workers further engage in heavy work.
    1. When there occurs a case which corresponds to those set forth in (a) of item 1; the time as listed in "Time for decreasing gas pressure after completion of work" column of Attached Table 1 in accordance with the classification set forth in the "Pressures" column and also in the "Time under high pressures" of the said Table on the basis of the pressure and the time under high pressure used for the final shift of work in compressed air.
    2. When there occurs a case set forth in (b) of item 1; the time as listed in the "Time for decreasing gas pressures after completion of work" column of Attached Table 2 in accordance with the classification set forth in the "Pressure" column and also in the "Time under high pressures" column of the said Table on the basis of the pressure and the time under high pressure used for the final shift of work in compressed air.
  4. In a case in which the employer gives the time for decreasing gas pressure of compressed air workers following the second time to the workers who work two shifts or more in compressed air per day, the times under high pressure of work in compressed air set forth in (a) of item 2 and (a) and (b) of the preceding item shall be those which are available by the addition of the time under high pressure used for the said shift of the compressed air workers concerned and the corrected time for compressed air workers.
(Control of Carbon Dioxide)

Article 16. The employer shall make ventilation and assume other required measures to ensure that the partial pressure of carbon dioxide is not more than 0.5 kPa in the work chamber or man-lock in order to prevent the hazards due to carbon dioxide.

(Control of Harmful Gases)

Article 17. The employer shall make ventilation, measure harmful gases and assume other required measures thereby to prevent danger and health impairment to workers due to harmful gases in the work chamber.

(Rate of Decompression)
  1. Article 18. When the employer reduces the pressure imposed on the compressed air workers in the man-lock, he shall comply with the items given below:
    1. The rate of decompression shall be 0.08 Mpa/min or less.
    2. When there occurs a case as described in (a) of item 1 of Article 15, the employer shall stop the decompression for the time set forth in the "Decompression" column or more, when the said pressure reaches that as described in the "Decompression" column in accordance with the classification as made in the "Pressure" column and the "Time under high pressures" column of Attached Table 1 on the basis of the pressures and the time under high pressure during the said work in compressed air.
    3. When there occurs a case as described in (b) of item 1 of Article 15, the employer shall stop the decompression for the period of time set forth in the "Decompression" column or more, when the said pressure reaches that set forth in the "Decompression" column in accordance with the classification as made in the "Pressure" column and "Time under high pressure" column of Attached Table 2 on the basis of the pressures and time under high pressure during the said work in compressed air.
  2. The provision of item 4 of Article 15 shall apply correspondingly in respect to the time under high pressures set forth in items 2 or 3 of the preceding Article, in the case of applying decompression for the second or subsequent time to a compressed air worker who is working more than two shifts of work in compressed air per day.
(Exceptions to Provisions on Decompression)
  1. Article 19.When the employer has a compressed air worker evacuate in an accident or rescues a compressed air worker who has become impaired in health, the employer is allowed to increase the rate of decompression as provided for by the preceding Article or to reduce the time for stopping decompression as also provided for by the same Article within the limits of minimum necessity.
  2. When the employer increases the rates of decompression or reduces the time for stopping the decompression in compliance with the provisions of the preceding paragraph, the employer shall quickly make the said worker enter into a recompression lock or man-lock after he has made the said worker evacuate or be rescued, and shall increase the pressure imposed on the said worker up to that which corresponds to the pressure used for the said shift of work in compressed air.
  3. The provision of Article 14 shall apply correspondingly in respect to the rate at which to increase the pressures when applying compression to the worker according to the provisions of the preceding paragraph.
(Measures Assumed when Applying Decompression)
  1. Article 20.When the employer carries out decompression on a compressed air worker in a man-lock, he shall assume each of the measures given below:
    1. The illuminance at the surface of the floor shall not be less than 20 lux.
    2. In case the temperature in the man-lock is 10ºC or less, the employer shall have the compressed air worker use blankets or other proper warming devices.
    3. In the case the time required for decompression is longer than an hour, the employer shall have the compressed air worker use a chair or other reposing article.
  2. When applying decompression to a compressed air worker in a man-lock, the employer shall inform in advance the said compressed air worker of the time necessary for decompression concerned.
(Recording, etc., for Decompression Status)

Article 20-2.When the employer shall have compressed air workers engage in work in compressed air under a barometric pressure of 0.1 MPa or more, the employer shall provide the man-lock with a self-recording pressure gauge, and shall prepare documents in which to record the status concerning each decompression and also documents in which to fill in names of the said compressed air workers and dates of decompression, for every time when applying decompression to a compressed air worker in the man-lock. And he shall keep these documents in custody for the period of five years.

(Communication)
  1. Article 21.hen the employer has compressed air workers engage in work in compressed air, he shall always station a liaison for contacting with the compressed air workers or with those who operate the air compressor, and also those responsible for other required measures (hereinafter called "liaison" in this Article).
  2. The employer shall provide for communicating devices by which the said liaison can communicate with the compressed air workers and those who operate the air compressor.
  3. The employer shall establish methods by which communication can be effected, even if the said devices break down, as provided for by the preceding Article, and shall put up a notice which indicates the methods at a conspicuous place from which the written methods can easily be seen by the compressed air workers, air compressor operators, and the said liaison.
(Inspection and Repairing of Equipment)
  1. Article 22.When the employer has a compressed air worker engage in work in compressed air, he shall make an inspection of the equipment, given in the following items, at least once at every period as described in the respective items, and shall make repairs and also assume other required measures when he finds probable hazards or health impairments to the compressed air worker:
    1. Air pipelines as described in Article 4, air exhaust pipelines set forth in Article 6 and the communicating devices as described in paragraph 2 of the preceding Article: one day.
    2. Valves or cocks regulating the feeding of air to the work chamber or the man-lock: one day.
    3. Valves or cocks regulating the exhausting of air from the work chamber or the man-lock: one day.
    4. Cooling devices attached to the air compressor for feeding of air to the work chamber or to the man-lock: one day.
    5. The devices described in Article 7-4: one day.
    6. Automatic warning devices described in Article 7-2: one week.
    7. The air compressor for feeding air to the work chamber or to the man-lock: one week.
    8. Pressure gauges described in Article 7 and Article 26: one month.
    9. Equipment for cleaning the air as set forth in the Article 5: one month.
    10. Electrical circuits installed in the caissons, diving bells, compressed shields, etc.: one month.
  2. When the employer makes an inspection of the devices, etc., in compliance with the provisions set forth in the preceding paragraph, provides for the repairing of them, and assumes other required measures, the employer shall record the results concerning the inspection, repairing and the other measures, as soon as they have been completed, and shall keep a short description of the record in custody for the period of three years.
(Inspection when the Air-Feeding Equipment Is Started)

Article 22-2. When the employer first uses air feeding equipment, when the employer disassembles and improves or repairs the said equipment or when the employer reuses the said air feeding equipment which has not been used for more than one month, he shall make an inspection of the performance of the said air feeding equipment and confirm that there is no abnormality in its performance before resuming its use.

(Measures to Be Taken in the Case of Accident)
  1. Article 23. When there is a possibility that hazards or health impairment to compressed air workers may have occurred due to a breakdown of the air feeding equipment, a flood, etc., the employer shall have the compressed air workers evacuate the caissons, diving bells, compressed shields, etc. 
  2. In a case set forth in the preceding paragraph, the employer shall make inspection of the presence or absence of abnormalities in the air-feeding equipment, the presence or absence of abnormal sinking of the diving bell, etc., the slanted status of the said devices and other items, and shall confirm that there is no possibility that hazard or health impairment may occur to the compressed air workers. He shall not have workers other than those who are specifically designated by the employer enter into the said caissons, diving bells, compressed shields, etc., until the said inspection and confirmation have been carried out by him.
(Measures Assumed for Submerging Exhausted Caissons)
  1. Article 24. When the employer submerges the said caissons by exhausting the air from the work chamber, he shall make the compressed air workers leave the caissons.
  2. In a case as described in the preceding paragraph, the employer shall make inspection of the presence or absence of flooding or generation of harmful gases, and also of the other items, and shall confirm that there is no possibility that there may occura hazard or health impairment to the compressed air workers. And the employer stall not have workers other than those who are specifically designated by him enter into the caissons until he has confirmed there is no possibility concerning the said hazard or health impairment.
(Measures Assumed in a Case in which Blasting is Carried Out)

Article 25. When the employer carry out blasting in the work chamber, he shall not make the compressed air workers enter into the work chamber till the air has returned to its original condition before the blasting.

(Prevention of Burns, etc.)
  1. Article 25-2. When the employer has a compressed air worker carry out work in compressed air, he shall inform the compressed air worker of the danger of combustion of substances combustible under pressures higher than atmospheric pressure, and shall furthermore assume the measures given below in terms of the caissons, diving bells, compressed shields, etc., in order to prevent burns and other danger from affecting the compressed air worker:
    1. The employer shall use lighting devices (lamps) with guards and other lamps in which there is no possibility that ignition will be made to combustible substances resulting from breakdown of the said lamps.
    2. In terms of switching devices used in electrical circuits, the employer shall use those from which no sparks or arc can occur.
    3. In terms of heating devices, the employer shall use those which have no possibility that they may serve as an ignition source for combustible substances when temperatures become high.
  2. When the employer has a compressed air worker engage in work in compressed air, he shall not have the said worker carry out work such as welding, cutting, and other work using either fire or arc (hereinafter called "work of welding, etc.") inside the caissons, diving bells, compressed shields, etc., provided that this does not apply in respect to the cases which are hardly avoidable owing to the nature of the work, and in which the work such as welding, etc., is carried out under pressures of less than 0.1 MPa .
  3. When the employer has a compressed air worker carry out work in compressed air, he shall prohibit the said worker from taking with him fire, matches, lighters, or other goods which give cause to fear that ignition or combustion may occur to enter into the caissons, diving bells, compressed shields, etc., and shall also put up a notice which describes the said prohibition as stated above at a conspicuous place outside of the man-lock, provided that this does not apply in respect to cases which are hardly avoidable owing to the nature of work and in which he is allowed to make the compressed air worker take with him fire, matches, lighter, or other possible ignitable or combustible goods which are necessary for carrying out the said work of welding, etc., which are carried out under pressures of less than 0.1 MPa, to enter into the inside of the said caisson, diving bell, compressed shield, etc.
(Limits concerning Digging Down below the Edge)

Article 25-3. The employer shall not have a compressed air worker dig down the portion below the edge of a caisson in depths or 50 cm or more in order to prevent hazard to the compressed air worker resulting from the sudden submerging of the caisson.

(Devices which Are Carried by Operations Chief of Work in Compressed Air)

Article 26. The employer shall have the operations chief of work in compressed air take with him a portable pressure gauge, flashlight, gas measuring apparatus to measure the concentrations of carbon dioxide and other harmful gases, and also signaling devices for an emergency.

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