Occupational safety instructions for working with liquid nitrogen and Dewar vessels

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Occupational safety instructions for working with liquid nitrogen and Dewar vessels

Occupational Safety and Health

Occupational Safety and Health / Standard instructions for labor protection

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Safe Operation

1. General safety requirements

1.1. When working with liquid nitrogen and Dewar vessels, personnel at least 18 years old who have been trained and instructed in safety when using refrigeration equipment are allowed.

1.2. Personnel must have a certificate for the right to work with liquid nitrogen and with Dewar vessels.

1.3. Personnel must know:

device and features of the work of Dewar vessels;
instructions for the technical operation and maintenance of Dewar vessels;
safety requirements when working with liquid nitrogen;
signs, causes, malfunctions in the work of Dewar vessels;
the impact on personnel of dangerous and harmful production factors that arise during work;
rules for the use of primary fire extinguishing equipment.

1.4. Personnel must:

perform only assigned work;
observe safety rules when draining and filling Dewar vessels with liquid nitrogen;
comply with the requirements of prohibiting, warning and prescriptive signs and inscriptions;
comply with the rules of internal labor regulations.

1.5. During the discharge and filling of liquid nitrogen, the following main dangerous and harmful factors can affect personnel:

increased pressure of liquid nitrogen;
low temperature, frostbite of open areas of the body when liquid nitrogen enters;
explosion of the Dewar vessel due to loss of vacuum, rapid desorption of gases during the heating of the vessel, and also due to the evaporation of liquid nitrogen with a hermetically closed neck;
condensation on liquid nitrogen cooled oxygen surfaces and ignition on contact with combustible materials.

1.6. Dewar flasks are double-walled containers made of aluminum alloys or stainless steel. Thermal insulation is placed between the walls. To increase its efficiency, the interstitial space is under vacuum, and the remaining gases are absorbed by adsorbent additives.

1.7. Personnel must use the following PPE:

cotton suit;
combined gloves;
leather boots.

In winter, additionally: a cotton jacket with a warm lining.

1.8. Personnel must monitor the serviceability of overalls, take them to the laundry in a timely manner, and also keep lockers clean and tidy.

1.9. Eat only in canteens or specially designated rooms.

1.10. Knowledge and implementation of this instruction by the personnel is an official duty, and their violation is a violation of labor discipline, which entails disciplinary or other liability in accordance with the legislation of the Russian Federation.

2. Safety requirements before starting work

2.1. Check by visual inspection the serviceability of the Dewar vessels, connecting hoses, shut-off valves.

2.2. Work in overalls, gloves. Hair must be tied back under a special cap.

3. Safety requirements during work

3.1. The operation of Dewar vessels must be carried out in accordance with the manufacturer's instructions for their operation.

3.2. It is strictly forbidden to operate or warm defective Dewar vessels in the working premises.

3.3. The Dewar vessel that has lost its vacuum must be freed from the stored sperm and liquid nitrogen, and then put on warming for three days in a room where people are not allowed to access.

3.4. It is permissible to close Dewar vessels only with lids intended for them.

3.5. It is forbidden to tightly close the neck of the vessel, since the evaporation of a part of the liquid nitrogen creates excess pressure inside the vessel and thereby prevents the ingress of oxygen from the outside air. In addition, the increase in pressure creates the risk of damage to the vessel or the release of liquid nitrogen.

3.6. It is necessary to pour liquid nitrogen into the Dewar vessel through a flexible metal hose with a diameter of 18 mm, the pressure according to the manometer in the transport tank should be no more than 0,5 atm.

3.7. Care should be taken to ensure that the flexible metal hose is lowered to the bottom, as the nitrogen jet can throw the metal hose out of the neck, and people working nearby may suffer.

3.8. From another Dewar vessel, pouring is carried out through a wide metal funnel, avoiding spillage of liquid.

3.9. During the filling process, it is strictly forbidden to look into the vessel to determine the liquid level.

3.10. Refueling is considered complete when the first splashes of liquid appear from the neck.

3.11. Particular care must be taken when filling warm Dewars, i.e. that have not been in operation or that have been thawed.

3.12. It is forbidden to fill Dewar vessels alone with liquid nitrogen.

3.13. Insert tweezers, canisters into liquid nitrogen slowly to avoid splashing caused by liquid boiling on contact with warm objects (nitrogen boils at a temperature of -195°C).

3.14. To ensure that the semen is always below the level of liquid nitrogen, the Dewars intended for its storage are periodically topped up.

3.15. The content of liquid oxygen in the mixture over 15% is not allowed, since such a mixture can cause ignition on contact with organic products.

The oxygen content is controlled by the GKhP-3 gas analyzer.

3.16. Drainage is carried out in an open special area in a safe place.

3.17. Do not allow wood, paper or other organic products near the drain.

3.18. To prevent contamination of the Dewar vessel, flexible metal hoses and funnels should be stored in covers.

3.19. To remove silt or solid particles, it is necessary to drain the remains from the vessel, rinse the vessel with pure liquid nitrogen and put on heating. Not earlier than after 3 days, the vessel is washed with a warm aqueous solution of detergent and rinsed with water.

3.20. Personnel working with Dewars and liquid nitrogen are required to wear safety goggles.

3.21. Premises where work with liquid nitrogen is carried out or Dewar vessels are stored must be equipped with supply and exhaust ventilation that provides an oxygen content in the air of at least 19%.

3.22. With natural ventilation, work with liquid nitrogen is allowed in a room whose volume is 7000 times greater than the volume of liquid nitrogen in it.

3.23. A decrease in oxygen concentration below 16% leads to dizziness, fainting and suffocation without any preliminary symptoms.

4. Safety requirements in emergency situations

4.1. In case of dizziness, fainting, the injured personnel should immediately be taken out to fresh air, if necessary, carry out artificial respiration and call an ambulance.

4.2. If liquid nitrogen gets on the skin, the affected area should be immediately washed with plenty of water.

4.3. In case of injury, call an ambulance, notify the master.

5. Safety requirements at the end of work

5.1. Remove protective clothing, wash hands with soap or take a shower. Report all comments to the master.

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