Massachusetts Institute of Technology
> George R. Wallace, Jr. Astrophysical Observatory

Safety-related Information

[ Location | Liquid Nitrogen | Photographic Chemicals | Pressurized Gases | High Voltage | Lasers | Machinery ]


Wallace Observatory isn't intrinsically dangerous, but it is isolated. If you were to be injured and unable to reach a telephone the consequences could be serious. Therefore, we strongly recommend that users not be at the observatory alone, and as a matter of course student observers will be assigned to observe in pairs.

Liquid Nitrogen

Nitrogen is used as a coolant; its boiling point at atmospheric pressure being 77K. It is hazardous mainly because of its low temperature. Gloves should be used when transferring nitrogen from one container to another, and care should be taken to avoid splashing it on yourself or others. Some materials may shatter if cooled rapidly; take care if you are cooling a substance you've never cooled before.

Another potential hazard presented by nitrogen is that it can cause asphyxiation if a large amount is boiled away in a confined area. This normally doesn't occur in a laboratory environment.

Finally, if a container of liquid nitrogen is sealed, so that the boiloff isn't allowed to escape, pressure will build up and an explosion may result. This situation must never be allowed to occur.

Photographic Chemicals

Photographic chemicals, when diluted to working solutions, are rather weak acids and bases, and are hazardous only if they come into contact with the eyes. Some people have adverse skin reactions to some chemicals, in which case plastic gloves should be used.

These chemicals are corrosive, so spills must be cleaned up and the affected area washed. The darkroom should be left clean after use.

Undiluted chemicals are quite potent, for example, stop bath is essentially concentrated acetic acid and can cause burns. When making up working solutions from concentrated stocks, be sure to read, understand, and follow the directions supplied with the chemicals. If you have questions ask for help.

Pressurized Gases

High-pressure gas cylinders of nitrogen gas and of forming gas are used in the darkroom for gas hypersensitization of photographic films and plates.

All cylinders must be secured against falling over, because if a cylinder falls and the value is severed, the cylinder may act as a rocket and cause severe damage and injury. Never use an oxygen regulator for any combustible gas. Never use a regulator for a combustible gas regulator with oxygen.

High Voltage

High voltage is used for photomultipliers.

Check for worn, abraded, or abused HV cables. Be familiar with HV cables and connectors. Ascertain that only HV connectors are used (the apparent physical appearances are similar to low-voltage connectors, but the HV connector body is longer). Turn off high voltage before working on equipment. Work with another person present in the room.


The lasers present are for optical work only, exclusively He-Ne lasers with beam powers of 5mW or less. These lasers are hazardous only because they can cause retinal burns if the beam enters your eye. Even a highly expanded beam or a specular reflection off of flat, antireflection-coated glass can cause a retinal burn if the bean directly enters your eye. The reason that such a low-power beam can burn your retina is that it focuses to a very small spot if the beam is collimated, so the power in the spot is high.

Avoid optical setups with unblocked beams and reflections; if this cannot be done, post signs to warn others of the locations of beam paths. Always use white cards or lenses to find the beam, rather than your eye, when working with lasers.


Machinery includes drill press, lathe, small hand tools. A shop course given during IAP and stressing safety is highly recommended.
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