valves to isolate the system to be opened, and tag these valves to ensure they remain shut while you are working on the equipment. Wear proper protective clothing. Do not try to take shortcuts and do not skylark. Carelessness has  been  a  factor  in  nearly  all  reported  mishaps involving steam. Observe all appropriate precautions. CLOSED COMPARTMENTS AND UNVENTED SPACES Never enter a closed space until it is certified safe by a gas free engineer. Closed  compartments  may  contain  hidden dangers, both to yourself and to the ship as a whole. One possibility  is  toxic  or  explosive  gases.  After  these spaces are opened, your gas free engineer will make sure that it s safe for you to work there. If  the  ship’s  been  damaged,  other  dangers  may exist. The manhole access cover to a damaged tank or compartment might be all that’s preventing flooding. Additionally,  water  entering  a  closed  compartment pressurizes the air already there. Don’t try to open a pressurized compartment or void without venting the pressure first. If you don’t vent the pressure first, the hatch  cover/access  will  fly  open  violently,  possibly injuring you or a shipmate. Check with your supervisor for  help  in  learning  to  recognize  these  and  other hazards. Consider all compartments dangerous if they’ve been closed for any length of time. If the bulkheads, deck,  or  overhead  are  rusted,  they  have  absorbed oxygen from the air. This means there may not be enough  oxygen  left  for  you  to  breathe.  If  the compartment  was  painted  before  it  was  closed,  the hardening paint has absorbed oxygen and given off carbon  monoxide.  Carbon  monoxide  is  particularly dangerous  because  it  gives  no  warning.  If  you’re working in a compartment that’s been closed and you notice a sudden feeling of weakness, drowsiness, or a slight headache,  call for help and get to fresh air. In storage compartments, several toxic gases may be generated by mildewing or rotting foodstuffs or by materials such as cloth, leather, and wood. Mildewing and rotting are speeded up when the space is warm and humid, such as when a ship is cruising in the Tropics or when an area has been flooded as a result of damage or accident. Carbon dioxide is frequently found in refrigerator spaces, even though the spaces are undamaged and the foodstuffs are still good. This condition results from lack of ventilation and the fact that foods slowly absorb oxygen and give off carbon dioxide. If personnel stay in such spaces longer than a few minutes at a time, they may be overcome and eventually suffocate. Sulfur oxides are acrid, corrosive, poisonous gases produced when fuels containing sulfur are burned. For example, aboard ship the primary producer of sulfur oxides is fuel oil, which contains sulfur as an impurity. Government agencies and industries have sought to reduce sulfur oxide emissions in three ways: 1.  Switching to low-sulfur fuels (those with less than 1% sulfur). 2.  Removing sulfur from fuels entirely. 3.  Removing  sulfur  oxides  from  combustion gases. To reduce the sulfur oxide problem on ships, the Navy developed a fuel oil called  Navy distillate fuel. Sulfur oxides produce an offensive odor and can cause  eye  and  lung  irritation.  Tanks  that  have  held petroleum products and compartments in which oil, gasoline, solvents, and organic products that have been spilled will contain the vapors of these products. Tanks  that  have  held  petroleum  products,  and compartments  in  which  oil,  gasoline,  solvents,  and organic products have been spilt, will contain the vapors of these products. You must assume that any closed space, double bottom,  tank,  cofferdam,  pontoon,  or  void  contains gases that can poison or suffocate you or can explode. (NOTE: Never enter any such space until it has been thoroughly  ventilated  and  checked  by  a  gas  free engineer to make sure there is no danger of poisoning, suffocating,  or  igniting  flammable  gases.)  Before entering  a  closed  space,  make  sure  that  it’s  been ventilated for 24 hours. Also, the gas free engineer must certify the safety of the space and recertify it every 8 hours while personnel are working in the space. Always have a person stationed at the entrance to maintain 19-9 Student Notes: