The primary hazard arises from the solvent's property of being highly or extremely flammable but several are also described as harmful and/or toxic.
Flammable Hazards. The most common fire hazard in the laboratory is a flammable liquid or the vapour produced from such a liquid. For a fire to occur requires i) an oxidising atmosphere (usually air), ii) flammable gas or vapour at a concentration within the flammability limits of the substance and iii) a source of ignition. Under normal circumstances oxygen or air will always be present and the optimal way to prevent fire is to segregate the vapour or gas from sources of ignition.
Some specific properties of flammable materials are:-
- The flash point is the lowest temperature at which a liquid has a sufficient vapour pressure to form an ignitable mixture with air near the surface of the liquid. Many common organic liquids have a flash point below room temperature e.g. acetone ( -18°C), diethyl ether ( -45°C). It is important to note that some flammable liquids will maintain their flammability even at concentrations as low as 10% by weight in water. Methanol and isopropanol have flash points below 38°C at concentrations as low as 30% by weight in water; HPLC acetonitrile/water mixtures of 15% to 30% acetonitrile are flammable.
- The ignition (autoignition) temperature of a substance is the minimum temperature required to initiate or cause self-sustained combustion independent of the heat source. A spark is not necessary for ignition when a flammable vapour reaches its autoignition temperature. Carbon disulphide is particularly dangerous in this respect with an autoignition temperature of 90°C. For Diethyl ether this is 160°C. and the material can be ignited by a hot plate.
Lower and Upper Explosive Limits.
- These limits define the range of concentrations in mixtures with air (or oxygen depending on definition) that will propagate a flame and cause an explosion. The lower values of these limits are normally well above the levels legally allowed as ambient in laboratories and workplaces but can be easily exceeded following a spillage. The upper limits of the flammability range offer little margin of safety because, when a solvent is spilled in the presence of a source of ignition, the lower level will be reached quickly and fire or explosion will occur before the upper limit is attained.
Sources of ignition.
- The most common sources of ignition in the laboratory are gas flames and heating elements but there are a number of less obvious electrical sources such as refrigerators, stirrer motors, heat-guns, microwave ovens etc. It also must be remembered that vapours from flammable liquids are denser than air and can spread over bench and floor surfaces to sources of ignition that are apparently remote.
Solvents are in constant use and the risk of fire is always significant with all the dangers that entails to personal safety and property damage. The level of injury could range from minor burns to death.
Transport of Solvents
The aim is to move solvents to and from laboratories avoiding the dangers of fire and toxicity that might arise from spillage.
- Winchester bottles of solvent must be transported in the corridors or lifts only in suitable carriers with a maximum load of two carriers per person or on a suitable trolley preferably with raised sides to restrain bottles.
- Plastic waste solvent containers must also be carried on such trolleys.
- A lab coat should be worn as a first barrier against spillage.
When collecting solvents from the Solvent Store:
- The described procedures for collecting solvents must be followed.
Only people acting in pairs may carry out solvent collections.
- No possible sources of ignition may be taken into the Solvent Store area.
- Any spills must be cleared up as described below under "Emergency Procedures".
Storage of Solvents
- Only the practical minimum amount of solvent may be kept in the laboratory.
- Solvents must be stored in non- flammable containers.
- Carboys of solvent must be stored in fire resisting cupboards when not in use, put away at night and not stored in or on the workbench.
- Solvents must not be stored with incompatible materials such as conc. nitric acid (oxidising agent).
- Waste solvent is as flammable as pure solvent and containers should not be left in the open laboratory.
Use of Solvents
- Solvents and other flammable liquids should be used with constant regard to the danger they pose to life and property.
- Under normal circumstances they should always be used in a fume-hood away from possible sources of ignition.
- Flammable solvents must never be poured down sinks.
Disposal of Waste Solvent
This Assessment should be read by everyone who uses solvents and the method of collection and storage should be demonstrated to newcomers. The use of solvents is a normal part of general Chemical training.
Level of Risk Remaining
Solvents are used in large amounts in much of Chemistry and this is unlikely to change so the flammability risk will remain. Constant vigilance is required by the users.
- Spillage, no fire
- Serious - toxic or large quantities. Evacuate and ventilate the affected area, closing doors and eliminating sources of ignition if it is safe to do so. Telephone the PSSO (x2691) or CAMPUS SECURITY out of hours (x2365) and OPERATE THE NEAREST FIRE ALARM POINT. Go to the PSSO Office to advise the emergency team of the nature of the incident. DO NOT ATTEMPT TO CLEAN UP A MAJOR SPILLAGE BY YOURSELF.
- Minor - Ventilate the affected area and eliminate any sources of ignition The liquid may be absorbed onto absorption granules available at the Fire Points or in the laboratory (have them replenished after use) and, as appropriate, transferred to a fume-hood to evaporate or to a suitable sealed container for waste disposal. In a well ventilated area such as a laboratory, the best procedure may be simply to turn off sources of ignition, ventilate, evacuate and seal and secure the room.